Well, it covers the cocking slot, doesn't move when you shoot.
Overpriced in most places, all the ones I have seen were plastic, the quality is pretty low when compared to the Spee-T, you have to cut your Flatline shroud for it to fit, doesn't work with all CAR stocks.
I think side cocking devices are a little pointless (having had one), but if you need one I'd go for the Spee-T Cocker if you can get it. The price is a little high, the quality a little low, and the functionality not much improved from the stock side cocking. It doesn't really quiet your marker, and it's not compatible with the LP kit or the EBolt kit.