I don't know how you can know what size of horse he is producing! he is only just coming 4, so his oldest offspring would still be babies themselves. It's too early to tell that. Even if they were breeding him at 2 years, his oldest offspring would only be coming 2 years of age!! Not full grown, and Traks take forever to grow, 2 years is too young to tell how they will finish out.
The only thing that bothers me about this, is that they have a contract and pay options right on the website, so basically what I understand is that they are willing to breed that stallion to whichever mare comes along. I don't like that idea, when you own a stallion, you should be picky about what you are breeding to, and should be selecting good representitives of mares to breed him to in his first few years so you have nice foals out there to present him in a good light. Most good stallion owners ask for pics, history on the mares and such before they accept payment for stud fees. If you breed them to whatever comes along, you could end up with alot of garbage out there, and it creates a bad image for your stallion as a stallion is only as good as his get. (I'm not saying your mare is garbage obviously, I'm just commenting on this situation) It's unfortunate as he looks like he'll be a fairly nice stallion, it would be a shame to muddy the waters surrounding him.