Why are they fire saleing them? It seems obvious to me, these kinds of cameras are set up on one production line and they have a production run of one. Once the M II comes out they won't even sell for $299 because everybody will want the new one. Canon have to get rid of the backlogged inventory or they write it off, at the moment I suspect they have the MII boxed up and ready to ship but are holding back to get ride of as many M's as they can.
Why would anybody buy one? Well it seems to me only a fool wouldn't. This is a fully compatible post 2012 APS-C sensored EOS camera, the perfect backup, or backup of your backup, depending on how anal you are. It shoots video, it uses your current lenses, it takes up practically no space or weight. It is fully functional in Group Mode with the RT flash system, the list of practical features goes on and on. Will the M II be "better"? Of course, but it won't be $299 unless Canon mess up on the stocking again and even then not for a year, and now they have the M nearly out of the way I am sure they have a much better feel for the M II market quantities.
At $299 with a decent 35mm f2.8 (equivalent) I can't see a down side to this camera bearing in mind the functionality and system integration. I was looking at the Fuji X100s or the EOS-M as a smaller camera, at less than 25% of the price for a much more useful (for us Canon shooters) interchangeable lens body the M seems like a no brainer.