I think vivi novas are the best thing since sliced bread. They are the only thing I have found that don't leak and give a consistent performance. Mine last an average of two weeks, but I'm not that great about cleaning them.
For the OP, I had mine for a month or two and just used the pre-bought heads, and it was a good deal. I got interested in rebuilding them with cotton wick because of the possible health issues with silica wick. I bought an ohms tester, kanthal wire, and some cotton candle wick. I watched a few videos and voila! Rebuilding them is really pretty easy, and the cotton wick tastes even better!
For $15 it's a steal. And if it doesn't work for you then you're not out too much.
Good luck!