-Are they comfortable?
I really like (and have always liked) how my wintec feels. Some people do and some people don't like them, it just depends on the saddle.
-Do they actually hold up?
Well.... I have the original wintec I bought that was a kids saddle and years later it's still functioning and in great condition. The one I have now has been put through the ringer (I'm REALLY hard on my saddles) and is in excellent condition. I can't stress enough how much it has survived. (Water, flipped over backwards in, thrown on the ground, trampled, the list can go on haha)
-Do you have problems fitting your horse (we have quarter horses)?
I've never had a problem. I buy them for my QH mare because I like the light weight on her back and it fits her to a T. I've used it on other QH's that were hard to fit and haven't had a problem (in some way I think the light weight helps with this). I've never put it on a horse and had the horse react out of pain to it unless it was a SEVERE misfit.
-If you have one, would you by another one?
Yes! I love it for my mare, and for me due to the weight, and though I still love leather saddles, synthetics are my go to when the leather doesn't work out. (Me and my mom can't lift heavy saddles anymore either.)
Personally I think they're perfect for trail/pleasure riding because of their weight. We go on long trail rides and I've seen that the horses the same age with leather saddles on that are heavy tend to tucker out faster than my mare and her wintec! Haha Plus you can beat the crap outta them and they still work like new.