This will not work anymore after July 1. Per their new policy you will only be allowed to go to 1 gym for $28 a month. If you add another gym you will only get a $5 discount. For example if the monthly for the second gym is $30, you will have to pay an extra $25 a month on top of the $28. A lot of people are pissed about this but the policy doesn't seem to be changing. I canceled mine since the gym I go the most is $20 monthly.
I researched how it works, basically they pay the gym you visit based on the day. For example today you visit gym 1, tomorrow gym 2, they each get a dollar per day I think, something in those terms.