I have the iStick TC60W like you, and would seriously consider the SBM as a second mod/tank kit - if I didn't have two TC60's already.

(I have a Subtank sitting on one of TC60's right now.) However, Kanger is going to be releasing a "Pro" version of the SBM that will have a new Subtank Mini that includes top-fill; not sure when it will actually hit the shelves, but several sites are showing it, so I expect sometime around first of the year. If there's one drawback to the Subtank, IMO, it's not having top-fill. The RBA is actually pretty easy to use; I'm just starting to build and it's super-easy to work on. The RBA and the available OCC coils for the Subtank make it pretty versatile for the price range IMO.