You mean "OK". Or did you see evidence that they are specifically quite happy?

The Amish are a cult.

Some of them are quite happy! Others are miserable; many are abused. It's a high-control group, that raises its children to believe the outside world as a terrible, scary place, and they are the only safe place to be.

Many people are happy in cults, or they couldn't function. But that doesn't mean that the cults are, overall, a positive thing.