I used a bunch of different KUIU stuff all year. My thoughts:
Merino 185 top - Super comfortable, no itch, Breathes well, dries fast, minimal odor. This is the only merino I have used so I can't compare to other merino. Way more comfortable than Sitka Core synthetic though. I always reach for the KUIU as my base layer now and my Core top sits in the closet. I've washed the top probably 7-8 times and there are a couple of small holes appearing near the collar that appear to be stress tears from backpack straps and possibly washing. Hopefully it continues to hold up overall. This may be typical for Merino, I'm not sure.
Attack Pants - what everyone else says is true. Really comfortable and a pleasure to wear. Unfortunately were a little too warm over the summer month, but they are my go-to pants outside of June-July-August. The fit is head and shoulders above the closest Sitka comparator, the 90% pant. Sitka pants are cut very oddly in my opinion. They bulge out at the knees and are tapered at the ankles. I gather that this was done to allow mobility in the knees while minimizing the amount of material used in the pants. The result is that they look funny and don't cover your boots very well at the cuffs. The KUIU pants fit like a normal pair of pants, and this works just fine for me. The simple cut of the KUIU pants (and the generous length) trumps Sitka's experimental cuts and "aggressive articulation" in my opinion. I only wear my 90% pants now if I really want to be in the optifade pattern.
Guide Jacket - Nice polyester jacket with simple no-nonsense design. Minimal zippers, pockets, and drawcords. I wear this jacket all the time, hunting or not. It is comparable to other high performance soft shells from mountaineering companies. I think the big difference is that they really tried to keep the weight down (hence the minimal bells and whistles). Does have pit zips which is nice. I would have preferred adjustable cuffs, but this would add some weight. Overall it is just a good solid jacket. Not blown away by it, but no major complaints. Compared to other hunting jackets though, I'd say its a clear winner. Another big plus for this one is the price - you wont find another softshell of this quality for this low a price.
Spindrift Jacket - standard Primaloft jacket - surprisingly warm for its weight. Biggest difference here is the simplicity of design - like the Guide jacket, there are no extra zippers, pockets etc. This is the big difference from the Sitka Kelvin. The Spindrift also uses the higher grade Primaloft One, whereas the Kelvin uses the Primaloft Sport (presumably this affects the warmth to weight ratio). I'd take the Spindrift over the Kelvin, particularly since, once again, the price is unmatched on the KUIU. It really is a fantastic deal for a Primaloft jacket.
Chugach pants and jacket - in keeping with the KUIU design philosophy, these are simple no-nonsense, minimalist designs. No problems at all with the waterproofing. Breatheability is typical (not that great - just like Gore Tex). Pants seem a little more rugged than the jacket which I like. I would prefer beefier cuffs on the jacket, but again this would add to weight. They say the Toray Dermizax this stuff is made from outshines Gore Tex in terms of waterproofing and breatheability. Can't say I've noticed a big difference, but I will say that the Chugach feels much nicer than any Gore Tex jacket I've encountered. Gore Tex tends to be more crinkly and plastic-feeling in my experience. The Chugach is softer and quieter (though not completely silent). Its possible that there are quieter Gore Tex jackets out there, I'm not sure. Again a huge factor here is price. A similar-performing system in Gore-Tex will set you back many hundreds of dollars more than the Chugach. Why pay more?
Guide gloves - Decently water resistant, very tough durable palms. Little bit of insulation. Nice close-fitting gloves with good dexterity, perfect for a misty fall day. I prefer as little glove as possible over my hands, so my go-to glove is my Sitka Shooter (very close fit and super dexterity). When it is a little colder and wetter, the Guide gloves are my next stop. A little more protection and no problems handling bow, rifle, shotgun. A good glove to have in your arsenal for the price.