I ordered an eGo passthrough and it just came in the mail today. This thing works great! I've been using a 5-volt (V4L) passthrough for over a year - maybe even two years (I'm too lazy to look through all my old files). I was quite happy with it and used their CoolCarts on it - I believe I read somewhere they are rated at 3.2 ohms. This combo provided a "sweet spot" for me.
When I left the house, I'd take a Riva or eGo and recently began using them with dual coil cartos. This was even a sweeter spot.
Right now I am using the eGo passthrough with an eGo mega dual coil carto. If these cartos last for more than a couple weeks, I will buy more. Shoot, I might even try cleaning them since they are a little more expensive than regular dual coils.
I've also been wondering if this eGo passthrough/battery can die like any battery, and if it does, will I still be able to use it as a passthrough? So, if what JohnnyElsewhere said is really true, that is very good news! It's a nice feature that you can unplug it and use like a regular eGo, but I will most likely only use it as a passthrough.
With all the passthroughs, I've had over a 3 year period, they stop working after a while I think because the wires in the cable break. The cable with the mini USB plug seems to be made well, but if it breaks, it stands to reason I should just be able to replace it with another cable of this type. I think I'll try that right now.........
I grabbed the USB cable with a regular USB plug at one end and a mini USB plug on the other that I use for charging a Kensington Power Pack (pretty generic like the ones used for Blackberrys and such) and it worked! So this little eGo passthrough seems to be one of my better e-cig-related purchases. Now, if that button just behaves, I'll be really happy.