While, I have not tried the m40x models, I have tried the 8084 (
njoy NPRO) and all I can say is nothing can be worse than the 8084. It produces VERY LITTLE vapor. The one thing that I can say as a positive for superminis in general is they generally vape the cartridge dry, thus no wasted
juice. Then again the cart only holds a couple drops of
juice to begin with
To be honest, and this is just my opinion so take it or leave it, I would say go with a 510. It really isnt that much longer and it rocks! Like I said, this is just my opinion so do what you want!