Read all of the Trog stuff, and on batteries, too...
All of the devices are (should) be rated at 5 volts, including your USB port. With that voltage applied to your ecig(s), they should all function the same. HOWEVER, most devices will lower available voltage as the 'load' increases...
Your computer power supply, and the number of devices you have hooked to all of your USB port, will determine what 'power' is seen by your ecig.
A 'straight' USB passthrough, ie, USB to wire to ecig, is the LEAST amount of power you will get, because everything else in the computer is 'sharing' the power to all USB. This should be the LEAST desireable configuration.
A self-powered hub, which is a USB hub plugged in to your computer, AND plugged in to the wall as well, provides good power to the ecig. If you plug directly into your computer, than you'd like the passthrough device with the small box and small battery inside it, in-line. That helps provide a more constant power to the ecig.
Any device that plugs into the wall socket directly, and then to the USB connector for the passthrough, will be very stable, where the 'load' will not vary and you should see a very constant 5 volts to the ecig.
If you can get a fairly constant voltage to your ecig, then everything else depends on the individual atm!
My preferences would be:
1. External device, plugged into the wall socket, directly to your ecig passthrough, and the passthrough has the in-line black box with the small battery inside...ideally, the power from the wall keeps the small lithium battery charged, providing a constant voltage to your ecig.
2. A self powered USB hub, where your ecig is being provided power from the hub, not from the computer, and the same passthrough as in #1. This is a second choice, because as you plug more devices into the hub, it will decrease the power to each device, ie, more 'load'.
3. A passthrough device, as in #1, plugged into your computer port... again, hopefully, the small battery in-line will stay charged from the computer.
4.The least desireable configuration would be a straight passthrough device, with no in-line battery, plugged directly into your computer.
John