It depends entirely on the gym. Lots are terrible but some are good. It's probably worth going once to see if you absolutely fall in love with it, but at those prices I wouldn't go twice unless you really do.
Training for sports (including body building) can be exciting, structured, fun and aesthetically pleasing. However, it does not train you to pull your family from a burning house, or pick up your children and run with them to hospital. An emphasis on specialism produces awesome endurance runners who cannot haul their luggage, and superbly strong strongmen who would collapse after jogging a mile. We look for the middle road; unfortunately it’s a hard road.
How is this so popular, it's pretty much some strength and conditioning training + HITT + some BS