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.