Yeah, they're great. I can shoot 'em in low light and a magnet on the bow's riser turns on the LED in the nock as it passes by. Puts out a nice bright red light and it definitely helps you track the arrow. Passing it over the magnet again turns it back off. Occasionally impact will turn them off (generally only if you fire off an arrow and it practically lands right on top of another one).

Oh... not those kinds of arrows, eh? :-p