Unless you can really sit a bouncy trot, don't do it.
My legs still ache three days down the line.
The high knee action makes for a VERY bumpy ride- and he moves more like a WB, as mentioned, rather than your typical frisian. I take my hat off to his owner, she makes it look so easy. All I can say is, if she didn't have huge knee blocks, I would have probably rolled straight off.
It was nice to rediscover stomach muscles.
I like to have a lot of horse under me, height and width wise. I'm not a fan of this 'modern' dressage horse that is appearing all over the place and looks like you could break it. But I also don't like feeling like I am sat on a sofa ;)
Before making the decsision, I would strongly advise you to try a few out, and when you go to buy, test ride as much as you can, and different breeds etc so you know what you really want.
Did I mention I love my own boy's lovely swinging but comfortable trot? :P