Which one are you referring to? As far as I know there are three flashhiders that people call "M-14 style."
1. The Choate "Birdcage." This has the same type of winged sights as the M-14, but the actual flashhider is much shorter, more like the M-16/AR-15. This hider is fairly popular on this site. The sights are regarded as being much better than the factory blade.
2. The Choate M-14 Style, which has the same exact sight as the above, but has a much longer flashhider and slots and so looks almost exactly like the M-14's. This model is no longer manufactured by Choate and is very hard to find, but very nice if you want your gun to look like an M1A. (I would like to have this flashhider, so if anyone wants to sell theirs, let me know)
3. Pescision Metalworks also makes one that has a winged post sight and has long vents. Originally, this was made to be used with a bayonet. Some (like mine) have bayonet lugs and all have a thicker diameter at the muzzle end to fill the hole in the M9 bayonet handle. This hider does not look nearly as good as the others but works superb at cutting down on the flash at night. It is very heavy as well, and this may contribute to greater accuracy, by dampening the barrel whip as others here have mentioned (but not proven, and I haven't tested it either). The sights on this one are also better than the original because they are lower (eliminating the wobbly rear sight) and darker (easier to see in glaring sunlight - the factory sight kind of dissapears in certain lighting conditions).