My MK low F is one of my favorite whistles, sounds great and is one of the most responsive whistles I’ve ever played. You can read a review of it here: http://pipersgrip.50webs.com/MKf.html
I highly recommend it, but unfortunately the waiting list is over a year with the maker last time I checked .
I don’t have any experience with other low F’s, but if they’re somewhat similar in characteristics to a low D from the same maker, I would recommend a V3, incredibly responsive, if a bit breathy in tone. If your looking for a very clean sounding whistle (no chiff or breathiness), you can’t go wrong with a Burke.
I have the Dixon low F as well, it sounds (to my ears) the nicest key for playing airs on whistle. I have no idea why this is - F is not a key I sing in and B or Bb is my fave pipe key for airs.
MK Low F. Beautiful. Loud, if ye need it. Wonderfully textured sound. Easy to handle. Brilliant player. In tune. Top notch!
Humphrey Low F. Quieter. Sound has a finer texture than MK…and is, to my ear, exquisite. Easy and fast player. Wonderful. Love it!
Copeland Low F. Brass. Strong volume. Brassy-pure. Sings. Clear sailing into the third octave. Slightly harder to handle, for me, because of the conical shape. (Like straight pipe better…) Great little whistle.
OS Chieftain Low F. Nice sound. Goes a bit too flat in the higher notes.
Susato Low F. Sent it back. (Like th Low D and Eb, though…)
True, in part, as of last fall I saw Grinter, Overton and Susato represented on stage by the Lunasa whistle contingent. Low F’s were Grinter and Overton, I think.
They were Grinters until one of the band sat on the bag with them and broke three Grinter low Fs (or that’s the story I’ve heard, anyway). They were replaced with Overtons.
If you are only ever going to get one Overton, the low F is the one to get. Followed by the Low D and the Mezzo A. And then all the rest. IMHO. YMMV.
I’m still getting used to playing it. It seems to take a lot of breath, but there are times when I’m able to “open up” and get a great sound without a lot of effort. But there’s also times when I’m struggling with my breath.