DD also did Tumble Tots and Gymboree. I thought Gymboree was much better than TT, not sure why but it did just should seem nicer, the staff more experienced and the equipment better. DD liked the fact that the parachute was a weekly thing, not once in a while like at TT. However it was more expensive.
As well as the classes you also get drop in times where you can go in - at no further cost - to sue the equipment.
DD did Gymboree from about 18 months and loved it. We mainly did the Play sessions, and she would join in, have fun, loved the singing and circle time, the parachute and the music. We also had a go at the music sessions which she also enjoyed a lot.
Yes, it has Gymboree linked songs, etc. but didn't make any difference to DD's enjoyment!
Was definitely worht it for DD. Depends on time of child yours is I guess though. DD loved joining in and getting involved, and was really good at following what the instructors said, and doing things at the times stated (like circle time etc).