Exercise classes and getting fitter and stronger

[PeridotCricket]

If I did three classes a week, like gates, circuits etc. Would that actually make me fitter and stronger?

Yes, assuming you do it properly and consistently then over time it will have an impact

Of course it would if you commit to it and do all the exercises properly & give it your all.

Yes. HIIT is effective, I started last summer and am fitter and stronger (despite still having a lot of weight to lose.)
You’ll feel awful during but fantastic after once the endorphins kick in.

Yes definitely! A good class will also be changing every week so your muscles keep being re-challenged. I usually do a circuits class and a yoga class weekly (as well as see a PT fortnightly ish, and do stuff at home - weights or running or yoga, whatever), and can often feel really challenged by the class work.