Hiya Kim ! depending on who's doing the measuring, the subtank nano is 18.5-18.6mm wide and 65.7-66.4mm high. It's rated at 15-30w on a 0.5ohm coil and 12-25w on a 1.2ohm coil. The sweetspot seems to be around 12-15w, reportedly gets hot above 20w.
At 3ml capacity, it's a little short on
juice-storage for subohmers and for MTLers the airflow might be a problem. It's said airflow can be tamped down to a draw similar to a protank 1 (which is still airy for me) but be prepared for warm vapor due to its stubby chimney. YMMV.
The mini RBA won't fit but the head itself is pretty easy to rebuildable - the coil leads come out the bottom and are secured by a little white grommet - but because of this grommet the coil can't be dryburned. Chasing rumors, I did read that the GS-H2/GS-H5 2.4ohm
coils might work, so I have some on order to see for myself. I'm also interested to see if the Aerotank V2 /V3 bases fit.