I usually play an open-holed Boehm silver flute, and I cover the holes with the pads of my fingers. I recently acquired my first low-D whistle, a Kerry Pro, and I do the same with it, covering the holes with the pads of my fingers. I’m struggling with piper’s grip; it doesn’t feel secure, quick, or comfortable. If I can already play reels at speed with the distal pads of my fingers, what advantage is there in piper’s grip? I think vibrato might sound better with piper’s grip, but are there any other good reasons to learn it? For the curious, my hands are not huge, but I stretch them further playing guitar than with my Kerry Pro.
The simple answer is: yes, of course. Then you have the choice.
Simply stop thinking of piper’s grip as a special thing with a special name. It’s not. Just scoot your index and middle fingers forward a bit, pivoting the hand around the pad of the ring finger. Voilà.
There should be no functional difference. Any techniques can be executed using either hand position. It’s just a matter of comfort and a relaxed, non-cramped grip. If your fingers aren’t flat across the holes, then switch.
Many players, including me, use PG on the lower hand only. That’s common.
Don’t go by your guitar experience. Different muscles, different movements, different stretch.
With the next low whistle you pick up, you may find a different hole spacing and be glad you can switch instantly to PG without a second thought.
What MTGuru said … while most players go to the Super Duper EZ Grip for the reach that it offers, it also allows a more relaxed hand position for both the wrists and fingers. I am an old guy who has developed arthritis in the fingers and other joints. The SDEZG is a godsend and allows me to play low whistles and flutes without any tension in the hands. I wish I had discovered it 40 years sooner.
I would encourage you to give it a go. Maybe a low D doesn’t force you to use it but you’ll be ready you suddenly want to buy that Howard low C or Goldie Bass A.
Feadoggie
Oh, right. I forgot the proper terminology. Don’t know what I was thinking.
You need to talk to the guy that changed the name! Oops, I keep spelling it wrong.
Does that mean I have to change my name? 
But do whatever works. I chose to use pipersgrip because I am double jointed in my fingers, and when I bend them the lock up while using normal grip. I haven’t had any problems with the grip.
If you’re happy with your flute player’s conventional fingering, stick with it. Don’t fix it if it ain’t broke! I don’t use piper’s grip at all either, maybe because I learned playing recorders all the way down to Tenor which is the same size as a low D. I try piper’s once in a while, but soon switch back.
I played a Low D whistle and a simple flute with a piper’s grip before I even knew there was a thing called a piper’s grip. Later, I was given a closed hole Boehm flute and just kept the practice up. I try to play with my fingertips and I’m getting better but I know someday, some formally trained player is actually going to see what I’m doing and either stop me or have the vapors.
FWIW, the secret to making the “piper’s grip” work is keeping the fingers straight, so they “hinge” at the first (biggest) knuckles, instead of flexing at the smaller knuckles and thus curving. Once you get the hang of it the fingers can open and close the holes of a low C or D whistle at least as fast as the finger tips do a tenor D.
This is how bagpipers (like me) manage to do those intricate yet quick embellishments on the GHB or smallpipes.
For what it’s worth, I don’t play low D with piper’s grip at all, and haven’t for the last 15 years or so. That said, the grip is clearly of benefit to a large number of people.
For me I find piper’s grip easiest but as you see from above others are fine without it. There are professional players (I’m thinking specifically of Jo Freya of Blowzabella, Old Swan Band and Token Women) who don’t use it.
I might make a distinction between the questions “Should I learn piper’s grip?” (as asked) and “Should I use piper’s grip?”.
The answer to the first being “Yes”, and to the second “Maybe”.
I’d thrown in my two cents since I haven’t noticed this answer to your question. I have huge hands but my finger tips are not as big as some. I can easily manage the spread since, like Paul, I started out on a keyless tenor recorder. But after playing several low whistles in each key, I find that sometimes the size of the holes, as on my wonderful new Goldie low D for example, are big enough that SDEZG simply works better. On others with smaller holes I don’t use it. So, as MT pointed out in a marvelous attempt at diplomacy, learn it indeed.
BTW, I watched a Celtic music special on local tv this weekend and noticed that the unnamed whistle and pipe player, who had a decidedly strong Irish accent, played his high D Sindt using a right hand only pipers grip. All three fingers contacted the whistle between the first and second knuckle only because this style enabled him to keep his right hand little finger down all the time as a stabilizing force. I tried it today and it’s actually not a bad idea.
ecohawk
One thing to remember when learning the grip is that knuckles at the bottom of the fingers should be level with the top of the whistle. This leaves the fingers truly flat across the tone holes. I find I can get much greater speed in finger articulations such as rolls, crans etc. with this grip. I actually learned tenor recorder fingering with this grip. My teacher was from Russia and had learned it as the prefered grip there. In a short time it becomes natural. I use the pads of the finger tips on the bottom holes for each hand. The top hand is angled so the pads of the second joint cover the holes. The bottom hand may be slightly angled to accomplish the same thing. Pancelticpiper had some photos up here which show this grip. Note that Louis Armstrong did not play trumpet with his fingertips and curved fingers, but with flat fingers, which he said gave him greater speed without cramping.
While I generally agree with that … Sometimes you don’t realize that what you’re doing is broke until you try something different, and possibly better.
I also learned Tenor recorder long before I started playing low whistles. And it’s apples and oranges. The recorder hole size and spacing (and sometimes lateral position) is different. Curved fingers are the norm (though Ted describes the exception - interesting). And recorder technique and ornament doesn’t require the percussive full-finger hammer/lever action that you want for trad playing, and that you can really only get with flat fingers, as both srleslie and Ted describe here.
My view is that if your hands are large enough on a particular whistle that your fingers don’t curl or curve in standard grip, you’re golden. Otherwise you need to switch to piper’s gr … oops, I mean Super Duper grip. 
Just wondering since this subject comes up often - should MTGuru’s original instructions for Pipers - Super Easy-SDEZG -Grip be made into a Sticky?
I know it helped me quite a lot and I always need to search for it. I guess I could bookmark it but then…
ecohawk
So I wonder, when did you all decide to try low whistles?
I started this journey pretty convinced I’d never have the urge to try a low whistle and the more I read about them the more I think I will someday.
First I’ll learn the soprano D of course, but maybe someday I’ll try a low whistle.
Just curious as to how everyone ended up with one? Another symptom of WHOA?
I think you will find that the path varies for each player.
When I started playing whistles in the late 60’s/early 70’s there were no low whistles to speak of. But, once the sound of the lower whistles became more prominent in concerts and commercial recordings I took notice and started buying what was slowly being made available in the keys below Bb.
Others may have been drawn to whistles by hearing a recording or performance on a low whistle. They might be motivated to start with a low F or low D right off the bat. That works. Some folks only play the low whistles. And low whistle do not seem to bring out the worst in family members and friends as high whistles may be prone to doing after a while. So it probably depends on what motivates people.
A reasonable approach might be to learn on what key whistle you have. And as you find music or musicians playing in other keys pick up whistles in those keys to play along. In other words buy another key when you need one. Before to long you’ll have most every key out there.
Feadoggie