Hi jellylsb,
Regarding the My Gym and My Little Gym, I have a few comment. My baby, who is now 1 yr old, she had attended trial class of MG and MLG when she was 8-9 mths old, I decided to go for MLG as I found that their gym place much larger, ie, babies can have more space for their crawling, walking around etc. Whereas MG will have more utilities to play with, ie. balls-pool or train.
For enhancing their muscles, I think MLG would be better as their trainer really teach babies to do things on their own (which I pretty like most). Now, she finished the Bugs class already and enjoyed very much. I also found that she learn a lot after 2-3 lessons, she now really enjoying the lessons and play with other babies.
That's my personal comments, nothing bias.