I haven’t read much of his stuff, but my brother has read almost everything he’s ever written.

He’s a fan.
More than just with Popcak, with any popular Catholic writer and speaker, I think we need to keep some things in mind.
He’s a Catholic for whom his Catholic faith is very important. And he strives to bring that faith to bear on his professional work. That is very good, and it often means that things that he says can be edifying and are generally consistent with Catholic teaching. Does this mean his every opinion is part of the deposit of faith that must be definitively held by all? No.
There are many things that good Catholics can disagree about. Parenting strategies is one of them. Does Greg Popcak’s overall philosophy contradict Catholic teaching? Not that I can see. Does that mean all Catholics have to follow his roadmap for being a Catholic parent or else they’re not really good Catholics? Of course not.
All else being equal, I’m generally in favor of more knowledge as opposed to less knowledge. So if you’re thinking about reading some of his books, I say go for it. I’m sure you’ll pick up some good insights. Just don’t ascribe to them any more authority than they actually possess. He’s not the pope and his books are not magisterial documents.
And I think I could safely say exactly the same about pretty much any popular Catholic speaker/writer.
Popcak also started the
Pastoral Solutions Institute. That’s a good place to go for anyone seeking counseling from a Catholic perspective. Even though I wouldn’t say I agree with him on everything, I think it’s great that he started a place like that. It’s great to have a place to refer people to get counseling from a Catholic perspective. That’s not always easy to find.