For ideal performance a 40 watt + regulated box would be best, something like a ipv mini 2 or istick 50watt depending on your budget. If your looking at the mvp3's you have options in that $60-70 market. I generally run my atlantis on a stingray clone or a regulated box at 33-35 watts.
Just looking at the spec's, i think the mvp3 is priced out of the market at $60+. You can get ipv mini 2's for less than $70 and istick 50's for $50 or less. The yihi chips are solid and just a more capable mod at that price point. They are getting dangerously close to vaporshark dna30 price per watt and i think hcigar is come'n out with a authentic evolve dna 40 board mod that looks like it might come in around $100. For $2 per watt I think you need to come with more than the ability to charge your iphone. The yihi board in my sigelei has been money. I won't know about the istick 50 till friday, $1 per watt is a nice figure.
If you already have some 20amp 18650's, I would not rule out a mech. That will keep a familiar sized device to what your used to. I know i generally don't carry around my box mods. The tubes mods are just more pocket friendly for me. I don't think a mech is a great fit for you, but i wouldn't outright dismiss it either.