The nice thing about kettlebells is they add a core element to pretty much every exercise.
I’ve used kettlebells, a traditional squat rack and a Smith machine. Traditional squats are definitely better than the Smith machine but I did not find the Smith machine unproductive. But, while Smith machine squats will work your major muscles, there are some ancillary elements of a traditional squat you do miss out on because you’re minimizing the stabilization piece.
If I were you (and I might be if I go back to Planet Fitness this winter) I’d do both Smith machine squats and lots of kettlebell stuff, including squats. Kettlebells rule!