Here's the FT piece:
Replacement Tank for SubTank Mini
Two small fill holes under the ring on the top cap, so you'd need a syringe or a needle-tip bottle. To me, that's a much bigger PITA than filling the wide open tank from the bottom. It would, however, solve the wasted tank volume issue. Some good reviews and some meh reviews on FT from those who have tried it. I could see using it if I know I'll have to refill the tank somewhere where I won't be able to wash my hands afterwards, since I can't seem to remove the base without getting juice all over my fingers. E-juice is like glitter to me - I seem to get a little on everything no matter how careful I try to be.
And no, it doesn't appear to be a Kanger product.