I am thinking I may have converted my mother AND sister to try e-cigs. I am currently checking out the Rivas (before they go off sale at LF since vaporpure is STILL out of stock) for them since they have longer battery life than just a reg 510. I see LF has both 901&510- what is the difference? The threading? Also, are they just as good as the eGo? I know they are basically the same thing. I just want to make sure I find a really good model that has a good batt life and that has the option of cartos too. My mother is still a huge skeptic so I want something that might make her happy and with less hassle than having to switch out batts all the time! Neither one can afford alot- so with the kits on sale at $30 I felt it would be a good starting point. I know I wish I would have gone for an eGo or Riva to start, but I do love the 510s I have 