It uses a potentiometer to adjust voltage output to the delivery device.
The below voltage levels as marked in roman #'s on the box are 'ish', meaning not consistently accurate.
1, 3.6v
2, 4v
3, 4.6v
4, 5.4v
5, 6.5v
The low voltage cut off claims to be 3.3v, again 'ish', mine fell between 3.127v ~ 3.272v.
The ' protection circuitry ' is rudimentary, much like an standard ego battery.
They claim it is able to handle 45a, but have not clarified if that is input or output. The solder joints were sloppy at best, wire used inadequate to handle 45a IMO, the fire button lost its 'feel' rapidly & became a source of mis fires.
I could go on for half a page...
Just me, a very poor choice for someone new to vaping.
Could be a very good choice for a person well versed in battery saftey, ohms/watts law and is looking for simplicity that understands there may be some things to keep an eye on & have the ability to repair.
Of course some folks love them.
" planing to vape around level 3 " doesn't mean much.
To get to your mentioned 120w on level 3 = 4.6v / .176Ω at 26a.
Keeping in mind the ' ish ' factor.