The iStick is a good option, but it is known for having a lousey 510 connection, if you are able to repair or replace the connector yourself no problem, I have on mine. Otherwise there is a version 2, 30 watt model coming out soon with a stainless steel spring loaded 510 connector, better option. There's also a 50 watt iStick model in the pipeline that is supposed have double the battery mah rating.
The MVP2 is also a good option, their 510 connector is also known to sometimes be an issue with some toppers. Otherwise there is a version 2 out, the MVP-20 watt with a spring loaded 510 connector, and a version 3 to be released soon with a spring loaded 510 connector and better placed fire button.
If what you have is working, keeping you off smokes, and you could wait a month, it may be worth the wait. Keep an eye open for threads of reviews by the early purchasers of the new models, see what problems are reported, and/or what they praise about the mods.