I'm an avid Subtank Mini fanboy, been using it non-stop for a few months now. But:
I agree with the naysayers when it comes to the MTL'ing on it. It's just not a MTL type tank IMO. The wide lung-hit encouraging mouth piece is the giveaway. Maybe modded a bit but out of the box, no.
You can MTL with it by all means. I've done it before with the lower ohm coil and some higher PG juice. The problem was the mouthpiece is too wide to get a good 'purchase' for drawing into your mouth. So I was having to draw it lung style just to get enough steam in my mouth to make the inhale part satisfying.
It's a spot tank but if I was to go full time MTL'ing I'd dig out my Nautlius or even the old iClear 30s. If I could get a much narrower mouthpiece to go on the Subtank though it would be a different story entirely.