I agree with IMFire. You won't be able to easily switch flavors with a cartotank. Because the cartomizer retains the previous flavor used, you'll need to use a new cartomizer with each new flavor. Most people devote a separate
tank to each flavor they use on a regular basis.
To sample or test flavors prior to dedicating an entire
tank to one, either a drip atomizer or a Nano clearomizer can be used.

510 drip atomizer

Nano clearomizer
A Nano clearomizer is a bottom-coil clearomizer that is the size and shape of a cartomizer. It holds only 1 ml of juice so is easy to sample flavors with. It can be emptied of one flavor and another added to sample the next one. These are relatively inexpensive. You add juice by removing the mouthpiece.