I take my son to Little Gym. We go to the one in Harpenden. I'm not sure which one you are talking about but for me its more like £15. (Have you factored in its for a semester rather than a term and there's a £20 yearly fee). Its extortionate but we weighed it up and, for us, its worth it.
The classes are in purpose built studios with great equipment - beam, asymmetric bars, an air track, boxes to jump off etc. The teachers are absolutely brilliant. If you miss a class (and let them know by 9.30 then you can make the class up at any other time.)
What you need to weigh up is what you are looking for in a class? For us, Ollie walked early but being quite podgy(!) was never a climber, very supple or acrobatic. He also isn't a risk taker. He has an end of July birthday so is young in the schoolyear. I also needed something that Dad or Grandparents could take him to. He's also a boy and needs to run and let off steam and 'was' not able to listen when he started at just before 2.
At almost 4 now, his confidence on the apparatus has grown. He is safe at swinging, balancing and climbing. Its a purely physical class. He's good at forward rolls and other balance moves. When he starts school he will be comfortable (despite being young) at PE etc and will recognise the equioment and the terms.
We trialled many kinds of classes from dance and singing classes, to tumble tots type of classes as well as drop in stuff and Little Gym met what we were looking for (in our area). It was purely physical. They could cope with our slightly 'wild' child with a short attention and slowly he grew into the class and with lots of patience on the staffs part he slowly learnt to listen and follow the class properly rather than run around. If there are challenging or shy etc behaviours, rather than ignoring them or getting irritated, another teacher joins the class to give 1-1 to whoever needs it which is great for the challenging child and not disruptive for the others . Its easy for parents/grandparents to accompany the kids as well and once they are 3 they go in by themselves.
Do a trial session and see how you feel. I hope that helps. It may not be worth the money for you or it could be what you are looking for.