If you want to buy it, please read this thread first.
I always used the $10/$15 pen batteries because it got the job done. But the low battery life was getting lower and lower. And I've found that I had to replace them because they keep breaking and not working. I just got sick of it one day and picked this up from a local smoke shop. 3 months later, I come online to buy the UNI Pro, because this battery is so amazing and I want the newest latest one.