I have both and like both. The MVP is full featured and, as has been said, is proven and accurate. I use it with my RDA because it is easy to keep standing up on end. I don't need it to crank out more than 11 watts - most of my flavors are great from 9-11 watts. I did have to send mine back due to the post inside the 510 connection coming loose, but it was covered under warranty, so I got a new one, no big deal. I bought another one, as well, just to have as a spare (and spare phone charger!). I really like it.
OTOH the istick is less accurate but at low wattage performs great and mates very well with my nautilus mini BVC, and the charge lasts a really long time. And compared to the MVP, it's very lightweight, not to mention smaller. So I always take the istick/mini rig out as a travel and on-the-go vape, and I am quite happy with it as such.
Since you guys have both now, you'll be able to assess how each of them meets your particular needs. I am thinking about getting my sis, who is new to vaping, an istick, though. A little simpler and will be easier for her to carry around with her. You might end up swapping devices w/your hubs. Either way, I think you will like both. The istick is cheap enough to get another of, though!