I believe many doubt the quality of workout they'll have with bands because a 100lb max resistance band just doesn't look as heavy as a 100lb dumbbell. I get it.
In some cases, I'd argue resistance bands are more effective than some traditional gym equipment. When you curl a set of dumbbells, there's barely any tension on your bicep muscles when you hit the top of the movement.
With bands, there's peak tension when you hit the top of the movement. This is what we want! Peak tension on the muscle when it's fully contracted.