Hello and welcome to the forum.
For starters when PGStaff speaks, people listen.
So definitely put a lot of weight into his post.
That said, I am not personally familiar with the Dirtbags or Impact baseball, but have heard about them, and seen a couple of their games in tourneys.
The reason I am even commenting is that they MIGHT be like a few other top travel teams in that they have multiple teams affiliated with them, but are not actually the top team.
The best way to describe it would be to imagine a professional team having a farm system with everything for AAA on down to rookie ball. If your kid is good enough to play for the Major team great, and they may not even need to pay. Where as the cost comes in when you sign up for one of the other teams thinking you will be with the top team(or a chance to move up to it), but wind up being stuck on the AA team. Now that in and of itself would not be a problem if the organization helped develop the kids, and tried to promote them. However at least two major travel teams I am familiar with use the lower teams to finance the top team, while giving little exposure to the players of those teams.
Worse still, they have no interest in developing your kid, and might have 4 other players on the same team that play his position. So you might be paying big $$$ and your son will only get 2 innings at 1st, then it will be bench time so the other kids get their minimum time as well.
Again I want to stress that the Dirtbags nor Impact have that reputation to the best of my knowledge, since I know nothing about how they are structured. But before signing up for any team, make sure exactly which team they will be playing for, and how many other kids are on the team at your sons same position.