The 306 is a Joye 306 (or Janty Minifogger) made by the same folks who make the 510 so it fits on the same threads. It is a little skinnier and over all smaller. It has a pretty solid exposed atomizer which on 510 batteries I feel gives pretty similar performance IMO. I've never used the actual 306 batteries but they are smaller than the 510 so I wouldn't expect them to out last it. Other than that my thoughts on the 306 and the 401 are pretty much spelled out in my previous post.