I would avoid this one. First off, he doesn't look grullo to me, he looks just plain old black (Would be interested to know what colour the sire is). This tells me the breeder/owner doesn't know as much as they should about breeding horses. Big red flag IMO.
Secondly, who sits a kid on a weanling? Then lunges the poor baby? That's just asking for problems. This looks like a baby with a lot of "un-learning" to do before he can start learning again.
Thirdly, his conformation doesn't look that spectacular from what I can see.