For those looking at getting into a bump fire stock, and not looking to spend the $260+ to get a Slide Fire stock there is a alternative that is now available for $99. From Bump Fire Systems the stock is polymer and as the same features that you see in most stocks now with an “on/off” selector that locks into the buffer tube and trigger finger rest.
Currently it is only available for the AR platform and for right handed shooters. An AK variation is also in the works, but not available as of this writing. Here is a marketing video, from them showing the function of the stock. You can also check out their site here: http://www.bumpfiresystems.com/
Look for a full review of one coming up soon as I just received one for testing and look forward to getting on a rifle in the next couple of weeks.