I have both.
Seen as a medium term solution, the MVP is superb. How long it lasts is hard to say, but even as a sole device it's got to do a year's (?) worth of charging.
People "rate" certain batteries/mods as being able to do x amount of charges. For example, a VV eGo battery should manage 300, but at what point does the battery start to show deterioration? For my needs, a Twist or Spinner shows loss of performance after even 100 charges.
The best thing about an external battery mod is having a pair (or three) batteries in rotation. I'm coming up to 1 year now on my 3 x 18650s and they are almost perfect. I wouldn't imagine that would be the case for an MVP. Much cheaper to buy some new batteries than a new mod, but hey.... MVP is $40 (?), even 6-8 months is less cost than all the other vaping purchases.