On the Istick vs MVP you need to also include that the MVP has been out for a while with very few problems reported. I personally can't use it much because it has a stiff firing button, but if you have normal hands that shouldn't be an issue. The Istick has pretty poor power management. I don't know all of the technical details, but if you watch P. Busardo's otherwise glowing review he explains it in detail. The result is that if you prefer to vape at lower voltage/wattage you're out of luck. There are also people reporting problems with the 510 connector.
As far as them both being disposable, that isn't a disadvantage for a lot of people. I don't want to swap batteries in and out, and I'm not alone in that. And if you end up deciding you need the high watts you're not likely to want to still have the same device in a year or two.