These boots are the best on the market, hands down.
Follow up - Almost 1 year later: I popped these boots on for a chilly morning clinic about a month ago, where many of these photos came from. After riding in my Ariat Breeze Half chaps and Mountain Horse show boots all spring and summer, these boots felt a little lose in the calf. I probably have also lost some weight, and was wearing a few less layers than usual. The ankle is also a bit of a shock after being in a tight ankled boot for so long, but they were comfortable. I will probably want to use some saddle tight especially on my smooth jumping saddle (pictured) but again, I think with some muscle increase (I know I've lost muscle in my lower leg... it swings like crazy all of the sudden) I'll be tighter in the tack.
Insulation: Thinsulate is the best you can buy - not too warm that your foot will sweat, but has kept my frostbitten-in-the-past toes warm in Minnesota's Artic Vortex -20+ degrees with windchill cold with wool socks and a toe warmer. In warmer areas, I anticipate these will be warm without being too warm. They are insulated all the way up the leg.
Fit: Foot is spacious - I wear a 9 in the Heritage Paddocks and a 9.5 in these boots. My older pair of Ariat winter boots (10 years old and still kicking - not water proof above the ankle but still great boots) are the same foot size and I found the toe to be more spacious in these, which I like. I like being able to move my toes and the space provides more area for the heat to build up. I wear mine with one or two layers of socks - smartwool alone or with a coolmax liner sock, and have been using toe warmers. I wear a M (14 1/2 - 15 1/2) in the Ariat Breeze half chaps and these boots were snug on first zipping but are comfortable and stay up nicely. They do seem to have stretched slightly so there may be some leeway.
Height: These boots are shorter than my usual taste in tall boots but have not caught on my saddle flaps in short, medium or dressage length stirrups. The heel does seem slightly higher than usual for boots, but they are not uncomfortable.
Materials, Aesthetics: The materials are quality and should last for a long time. I like that they are suede and leather, not synthetic, which has cracked on me in the past. The leather foot is water proof and there is a membrane in the foot which crosses the zipper around the ankle - sometimes the zipper catches here, but usually I just change the angle (put my heel down) and the zipper glides smoothly. The ankle is flexible and I am able to wear spurs and use them with finesse because I can feel and move my ankles. Inside calf is grey suede, which I believe I will rub smooth in the future but don't foresee it degrading or developing holes. Some of the nylon parts (outside of ankle, top) is a slightly purple hued grey, but the boots are not PURPLE as they look in some pictures. Zipper is quality and doesn't catch except sometimes around the ankle membrane, which is easily resolved. These boots are waterproof but I wish the zipper was wholly waterproof as I've stepped in some deep drifts and felt a bit damp because the snow was above the waterproof membrane.
I did think they looked a bit clunky on others, but love them as they are warm and not clompy/heavy/oppressive to wear on the ground or in the tack. The round toe still allows for a narrow profile and I have never had concerns that these boots will catch in my stirrups as other brands have. I was dragged in another brand of winter boots several years ago after they turned and wedged in my stirrup after a fall. I have never felt these boots get stuck or wedged, but still ride in break away stirrups in winter as a preventative. Comfortable on the ground and to ride in, I am recommending them to anyone who hates cold feet but wants to ride or work through the winter