Personally, I think for the price of Tumble Tots, I would look at a local gym club to see if they run preschool classes.
My DD went to our local gym club from the age of 18 months.
At the gym club, it takes place in a safe gym - where there are sprung floors, and bouncy stuff everywhere! TT happen anywhere, so the environment may not be as safe.
At the gym club, the instructor is a qualified preschool coach, who is registered with British Gymnastics, has undertaken training to ensure that what she does with children is safe and age appropriate, following their early years 'FUNdamentals' programme. At TT, it is a franchise and any Tom, Dick or Harry can buy the franchise. Indeed on their website it says, "Experience of working with children is not essential, but running a business in a child environment requires individuals to enjoy working with children and their parents."
Because the gym classes are run by professional gymnastic coaches, the children get to do so much more than what they can do at TT. I've always done gym, but another mum who has moved over from TT is surprised at just how much they are expected to do in a gym class. My DD2 is 3 now, and she is perfectly capable of walking along the high beam alone (although a coach is always nearby in case they are needed), jump / step over things on a low beam, do leg lifts on a bar, head stands against something soft, front and back roly polys and the list goes on....
If you can go to a gymnastics class, then I personally would favour that option, as they do learn so much....not sure I'd bother with a tumble tots class though.