The Silver Bullet does 3.7v and 6v. You need to get different batteries. The BB does 3.7v with batteries and 5v if you buy the Pass-Though and have a 2.0 powered USB. Their are many adapters for that. Oh the BB also does 6v but I have not done this b/c the batteries are unprotected. Also they (Rob and Chad) have been talking about coming out with a PT for the Silver Bullet to do 5v.
I have the set and like them for different reasons. The BB is small and is great to have on the go. The SB and BSB have giving me no troubles at all, but they are bigger. The button is the reason I went with the Silver Bullet in the first place. Doesn't feel or look like a $0.05 button that would activate anytime it wanted to. Just don't drop it. I have a battle scar on my SB and BB. Trying to keep the BSB nice and scar free.
He should have stock back in a couple of days. I know he has been keeping Chad busy and the holidays must have taken it toll on his inventory.