You really have to keep a lot of air in it for it to move as quickly as it should. I have a pretty good platform (not a cheapo) and, even so, it takes a pounding to keep the speed going. Also, it no longer holds air and I have only used it on occassion for a few months.
P.S... I am not a beginner on the speedbag. I have experience with "good ones" and this one does not fall into that category.

If you wonder, I have this platform
http://www.karatedepot.com/bx-sb-33.html
and it is installed securely.
  

I like this extra small Everlast speed bag. It is a very quick speed bag and does take some getting used to. But once you get the hang of it, you will become addicted. I would recommend it to anyone who is interested in increasing hand/eye coordination.   

I've got this bag. Haven't used it yet because to be completely honest, I am intimidated by the speed bag. Once I've given it a go, I'll give a complete write up on it.  

Throw away your beach ball and train with the smallest and best bag going.Everlast is apparently re-vamping it's speed bag lineup, so you can steal this mini marvel for a mere $30. The flat leather welts enable you to punch away from the first day without clumsy break in time other poorly designed bags demand. This bag is not for everybody though. Only long time speed baggers are going to get maximum performance from this. Watch the Speed Bag Skunk videos on YouTube and see this is the bag he uses, while Everlast currently has him evaluating a newly planned XXS model.  

This speed bag is pretty good. I originally wasnt even going to get one of these but the home gym i got had a speed bag platform on it so i picked one up. I like using it, the outer layer is touch and feels good to hit. The bladder hasnt ruptured oor broken yet eaither. Hooking it up was pretty simple as well. A good buy.