Does anyone here really have a humble opinion?
Didn't we all learn that R&D stood for Ripoff & Duplicate?
But, to be honest, I have no problem using similar language and exercies as long as they are done correctly and are appropriate for the student.
As long as the language and exercies are grounded is solid principles I'm for it.
Sometimes when coaching people going for LII exams I am asked if they should use something that is widely used. My response is always, as long as you REALLY understand what's going on and do it correctly.
The problem with the guy with his kids is that he probably had no clue what he was talking about and how the suggestions he was giving his kids fit into an overall learning situation.