I have picked some up and they seem to be better than the Sports medicine ones as more breathable. They have a better lining than the SM ones so do not look like they would get so sweaty.
I have large on my TB on hinds and M in front but not in that style.
I have the air cooled eventing boots and over reach boots and think they are fantastic and also good value for money. I would ring them up, their number is on their website. They are really helpful, advised me which measurements to take, rang back, they told me the size and they arrived and fitted perfectly. My boy is an id x tb and 16.2hh and a big chap and in the event boots he is a large on the hind and a medium at the front.