I use the older Magnetic "M" series on an 870 in low-light conditions ... just a help to reference the end of the muzzle against dark backgrounds.
The M-300 fits most Remingtons .. and the magnets are strong ... haven't lost the one I use on the 870 in about 10 seasons, nor the one I occassionally use for Sporting on a Beretta in a bout the same interval. I take them off for most shooting in normal light conditions, however.
As an aside, you'd be surprised how well you can shoot with no bead(s) at all,
and many have affirmed just this after noticing their bead had gone missing ..
and they couldn't tell when or how long it had been gone !
In low light however, every bit helps.