The only thing I can think of to recommend would be ce3 clearomizers. Now, they're not going to be rebuildable as in buying replacement heads, but the base is basically the same thing as the heads on the vivis, etc, and can be recoiled/wicked the same way if you like tinkering like that. They are more discreet looking than a larger tank style and generally (I say generally as I have not played with every single knockoff of every part, but mine have always worked) fit in the stock ego cones and use standard drip tips.