I also have Ariat heritage paddock boots. As far as comfort and function goes I love the boots. I've never had a problem breaking them in, and they perform as they should.
I don't know how long paddock boots are expected to last, but 4 years is about the typical lifespan for my Ariats. The first pair that I had (besides the ones the dog chewed up...) were lace ups that I wore when I was just taking weekly lessons, and I would guess they lasted about two years before the rubber sole completely separated from the upper part of the boot. The next pair that I got were lace ups, and those lasted me all through high school before they began to crack. The cracks gradually got to the point of needing replacing, but the zipper broke in one and that did them in. The pair that I have now has lasted just over 4 years, and cracks are just starting to develop them. I would be shocked if in six months I hadn't had to buy another pair. I'll probably go with another pair of Ariats.
Maybe they wouldn't develop cracks if I cleaned and conditioned them after every ride in our dusty arena. That's just not going to happen though... but $100 spent every 4-5 years on riding footwear doesn't seem too bad in the grand scheme of things. Also, just because of ease of putting them on I will never buy a pair of lace up paddock boots. Zip up for me all the way!