This is precisely my situation. I still play my GHBs and I like to compete (grade 3). I played for about 10 years and just started Ups last February.
Fingering: I was afraid of it at first, but it worked out fine. This month, I finally had someone tell me to move my high hand inward to play with the second segment instead of the pads on the tips. That was hard, but a few hours later I can play everything again. Last night at band practice, I tried playing a bit using uilleann finger positions and it was amusing… Still going to keep them separate…
I learned NOT to try to play tunes on both instruments. Maybe this works okay for others, but it just ruins both cersions for me. I play a mean Mason’s Apron on GHBs and when I first got my UPs I learned it using UP fingering… what a mistake… I still goof that up now on GHBs.
Bellows: I played bellows smallpipes for several years, so that was not new.
Reed making: ugh… I get one good reed out of every dozen or so, but I understand that isn’t so bad. I have come to enjoy this little craft and hope to be good at it…one day.
I didn’t find getting the second octave too hard, but balancing the chanter so that two octaves are in tune really befuddled me at first.
I think playing both complements both in some general ways: my fingers are stronger and more controlled, I think.
Downside is keeping up practice on 2 instruments. I’m very hooked on these UPs and my band just came out with fall music… hard to tear away to work on GHB stuff.
I am very, very much enjoying this instrument and wonder… much as I still love playing GHBs, would I have ever bothered to learn GHBs if I had learned UPs first?
Of course, another point might be that, since I don;t have a teacher, I could not have made the good progress I have made on UPs had I not already been proficient on the GHB and SSP.
I think I stored some impressions of my experience starting the UPS somewhere on this forum for future reference… try a search under my user name djones…
Have fun!
DJones