Cabbage played in the league. I'll echo most of what Goosegg and BOF said. The format is quite different. The quality of players is very good. Most often, there is a D1 or likely draft pick pitcher on the hill. The Cardinals seem to be the cream of the crop as far as organizations go but they run two squads - red and blue. Red is mostly higher profile players. They get a crazy amount of players show up for their tryouts and they have quite a bit of info on their website. Son played with the Wahoos and this may be another option based on were you live. Most send teams to Arizona Fall Classic and there is also a big scout tourney. Some run summer teams in a totally different manner than the fall teams. Most have websites. This league will definitely let your son know where he stacks up against good players.
I'm a bit out of touch with it the last couple years. I heard there may be a movement toward some younger teams but not sure.