Photos don't really offer much opportunity to give much of an opinion TBH. The write up sounds good, but who knows? But if not too far from you why not go and have a look and see.
Sounds nice but also sounds like being described by a novice..... not sure if its just me though. Plastic snaffle doesnt sound correct and why mention the martingale if he doesnt wear one???
I don't think the photos do him any justice. He doesn't tuck his forelegs up in the first pic and you can't really see much in the other pics. I would email the owners and ask for more specific pics.
Also one thing that stood out to me is that they have only owned the horse for 5 - 6months and they say he isn't big enough??? Surely he would have been to small when they brought him? He wouldn't have shrunk lol. This sets off alarm bells in my head. I don't think it is ever a waste to go and look at a horse but I would really get more info and pics out of them before travelling to see him.
Hope this helps.