Mech mods are the batteries or PV as most call it and you can use your existing tanks on it. Only thing is that it does not have any electronic parts on it so it will deliver only whatever power left in your battery as it runs down. I suggest you read more before jumping on to mods as it is not for everybody.

What you have seen the guy using is a dripper tank or atomizer (or atty) which is rebuildable to low ohms for use with mech mods but not everyone likes using a dripper. Best you carry on with what you have for a few weeks then only decide what to get next.