The Kanger eGo battery, from what I've been able to find, is a 3.7 V regulated voltage output (normally I'd figure this is just the "nominal" voltage rating). This is very good for single-coil Kanger devices such as the EVOD (1) and mini PT2, although maybe not as good as a small variable voltage battery (the single button controlled type are cheap and also seem tailor-made for single coil Kanger). It will not fully drive EVOD 2, PT3, or Aspire stuff which can need 4.2 volts or more (4.2V will burn juice/coil in regular EVODs). They also can need more than 10 watts. A *good* Spinner type battery is usually sufficient.
The iStick batteries are great, but they do need an adapter (included) to go to the eGo thread of most of the above mentioned clearos. Even with a 510 thread clearo I wouldn't want to run around with one in my pocket the way I can with a small, cheap EVOD. Also, the iStick 20 has a flaw that the settings may not go down far enough for mini PT2's (at least, the setting needs be lower) which the 30 watt doesn't (don't know about the 10). It might be best for now to get a small easy-portable/backup unit and save for something bigger next month.
Kanger just came out with cotton wicked, vertical coil versions of the dual coil form factor coils. I don't know if these are better than the Aspire's or just Kanger playing catch-up. Of the single coil Kanger style, I like the mini-PT2 for clean-tasting, possible tank-cracking juices, but the EVOD has more flavor -- with some tobaccos, perhaps the most flavor of anything ever made (yeah it makes no sense).