Battery life is what everyone is working on. While the little stock
batteries that are the shape of a tobacco cigarette are getting better, they still run down frequently. When I first started (5 whole months ago), I brought a spare 510 battery and a 510 mega battery with me when I went to work and I also had a USB charger. As soon as I ran one battery down, I'd plug it into my computer to recharge.
A PCC like the charger case the Blu comes with does the same thing if you don't work next to a computer all day. But if battery life is the main reason you are buying a Blu, you can do better buying something that doesn't have a short-lived stock battery. As Domino suggested, you can go with an eGo -- a 510 with a better battery than either the Blu or the standard 510. Or you can go straight to a battery mod -- I have a Little Chuck and I just toss an extra charged battery the size of a C in my bag and I'm good for 15 hours or so. (Sometimes I toss 2 in my bag.)
As for the button on the 510, that's a manual. You choose how long you want to inhale. If you want to drip, you won't destroy the battery (as you would on an automatic.) But 510s are available with automatic batteries if you want. Of course, some automatic batteries have been know to fire up when there's a loud noise (the sound of inhaling them is what starts them.)
I'll bet that you have to take the atomizer off the battery when you put your Blu in the case. Once you do that, you can't use the battery (the circuit or whatever isn't complete.) The same thing is true of a 510. Take off the atomizer and you can push the button for hours without using up the charge.
But the bottom line is what's right for you. If you think a Blu is a good PV for you, get it.