Great pack, nice thing I like is all 3 pack sizes fit the frame, I have all 3 for different uses. I hike into spike camp with the 6000 loaded and have the 1800 bag (only 9oz.) thrown in to thrown on the frame to use for a day pack.
I've used guiding and on my own a mystery ranch crew cab, several Dana designs terra frame, terra plane, Eberlwstock black widow, Barney's Sports Chalet, and cabelas frame packs. Of these my Kuiu Ultra is the most comfortable (for me) certainly the lightest, and probably most fragile. I have mostly used the 1800 bag but with ability to pack stuff between the frame and bag it works great. It is also very good riding a horse (short frame). It is NOT bombproof like some of the others on my list but for normal use it's great. I don't think you can go wrong with these newer lighter packs like kuiu or stone glacier for ordinary hunting use.