I have the Prodigy with both 801 and 901 adapters and love it. It's a little bigger than a Mini-Maglite flashlight, both in diameter and length (with atomizer attached). One advantage of the 5V system is that I have several atomizers that just got too "wimpy" with regular 3.7V batteries but they produce tons of vapor with the Prodigy. I still use regular batteries when I'm out and about. With a good atomizer they are still quite satisfying, so I can't say the 5V system has "spoiled" me. Not yet, anyway.
I also have two Puresmoker passthroughs and they are, shall we say, monuments to over-engineering.

Don't get me wrong, I love these PT's, but they are MUCH bigger than the Chinese ones. You won't be able to coil it up and put it in your pocket (unless you have a very large pocket!), but after all PT's aren't
supposed to be portable. The Puresmoker PT has a manual switch and runs 5V direct from the USB port with no inline battery or voltage-dropping circuitry. The heavy cord (think TV or CB cable) provides the full 5V from USB with little or no voltage drop so they perform noticably better than the dinky little Chinese versions. They cost more, but like the Prodigy, they have interchangeable adapters for different atomizers. They appear to be built to last forever.
Puresmoker currently has 801 and 901 adapters available for both the Prodigy and the passthroughs. You can buy one Prodigy or PT and add different adapters for versitility. The adapters are
completely sealed so no juice will get into the switch or battery compartment. Adapters for the 510, M401/2/3, and RN4081 are planned for the near future but I don't believe they are available at the moment. I believe you can pre-order them, though.
TT33