Sure, you can buy a Costco pack of Energizers and blow those puppies in a few months... or you can get a little extra voltage for faster solenoid reaction, longer usable battery life (as the battery dies the voltage drops slightly... the extra voltage in these helps you in those tight situations).
Don't forget that this NiMH battery is rechargeable, without developing a "memory." You can charge it fully, quick-charge it, half-charge it, upside-down charge it or just plain not charge it at all! Hustle Paintball doesn't recommend the final "solution," but it can be done, and your battery's chargeability won't be affected by your charging habits, as the older NiCd batteries often were.
If you didn't understand the techno-babble, don't worry about it - it was all good stuff. You can use this battery with anything that accepts standard 9V batteries. Don't forget to pick up a charger!