Seeing as i own both, my thoughts are that i really would get both if possible. .3 ohms on a mech is great! the feeling of a .6 ohm coil at 6volts on the hexohm is also incredible. Essentially there is a place for both and for me its on a daily basis.
But if i had to chose one to have for good...hmmm I would get the hexohm and give up all my mechs to have it.
The hexohm is an awesome device, the OKR T10 chip set is great, it really is. The hexohm takes a bit more knowledge in my opinion, seeing as you need a pair of batteries that are new just for that mod and you need charge them at the same time and you need to switch their position in the battery sled every time you discharge them down to needing charging. The twin 18650 battery life is great i can vape at 60 watts 10 amps all day and well into the next before batteries need charging. get a hexohm you will not be disappointed.