Absolute waste of time and money, God knows why whoever thought this idea up actually continued after testing them, Tennis Balls or squash balls are a good idea and do work, paving slabs do in most situations also. We had a problem in a new club we were doing a night in a while back and everyone of these ideas didnt help one bit as the dj booth was actually on a upstairs floor and once you had a few hundred people bouncing around it was a nightmare so one of my mates had an idea, we took a few pieces of foam, The kinda stuff that looks like egg boxes or acoustic foam, and put a block under each deck about 4 inches wide, Kinda worked the same as these inflatable things other than the fact it was a lot more stable, Probably not much use for you on this occasion but worth sharing cos you never know when it might be needed