Prebuilt coil units tend to be associated with the tanks they fit. There are some cases you can fit a different coil but not many. Surprisingly, different tanks can be a lot different even with the same coils.
I do like the single coil Kanger types, especially with the EVOD. Most juices get good flavor with it and a some just explode. The prevailing idea is that more power gets more flavor, yet these things slay at 5.2 watts or so. They do have a bit of their own flavor, especially with the silica wicks, not a clear and clean flavor by any means though. I've done cotton rewicks on brand new coil units, now rebuild them with Fasttech coils.