One thing to consider, IMO, is the main reason for a tank is not having to fill or top off the carto
repeatedly. The 19mm OCD is a good looking tank, especially for something like the Twist, but it
doesn't have a lot of capacity. The 25mm tank should be a good match for the Vmax and has
much more capacity to last all day on one tank.
You say you are hesitant about tanks because you are just getting used to cartos; well, the
tank makes using cartos easier. They were made to give the carto more juice capacity,
giving it that "just filled" performance, and only having to fill tank once a day ( hopefully ).
Another benefit is, keeping the carto moist should prolong its life.
A tank will be even easier to use if you get yourself a tank filling tool like the "Slap yo Mama"
from Big Daddy Vapors. It will prevent the carto from tearing the inner o-rings when inserting
the carto, it allows you to fill the tank completely straight from a std dropper bottle ( no need
for syringe or special tips ), and will allow you to change cartos even with juice still in tank.
Very important to keep in mid, you WILL need to experiment. There are many factors in how
well a tank works. The type of juice, the type of carto, how your carto is punched or slotted,
even your environment; these all effect how well the carto will work in your tank. As long
as the tank fits together well and fits on the carto well to prevent leaking, tanks are all the same.
Performance depends on the carto and juice that you use.
note - Some people still "slot" their cartos, but slots are rough on the inner o-rings.