Those are cheap, unreliable systems compared to a real weaponlight.
My experience indicates differently.
I've used various Streamlight rails on several different shotguns- FN/Winchester, Remington and Mossberg. And I've used several different rail-mounted lights, both Xenon and LED- Streamlight M3s, LEDWave Z5s, Streamlight TLR1s and TLR2s so far.
They ARE real weaponlights. And they are plenty durable, even on a shotgun. Of course, being rail mounted, they can easily be removed for practice sessions (which should always be common practice, even with SureFire's integral fore-end lights). In fact, the company makes a 'practice plug' to replace the batteries and flashlight for daytime practice sessions, and suggests that users employ it-
For extensive practice or training, SureFire offers a screw-in plug to replace the lamp module in the dedicated forend. No point in subjecting the light to more pounding than necessary. -
http://www.surefire.com/maxexp/main/co_disp/displ/pgrfnbr/443/sesent/00
I don't like SureFire fore-ends a whole lot myself- been using them since they were marked Laser Products, and they crowd my support hand. There just isn't enough room there for my paw and the light housing too. And since my dear wife absolutely insists on full length field type forearms on the house guns, all the SureFire equipped 870s are in the safe.
Right now we use 870s with no magazine extensions as house guns, so the 'ring mount' type rail (
http://www.copsplus.com/prodnum2264.php ) is employed on them. I've used these literally ever since the prototypes first appeared some years ago with no problem- they're plenty sturdy.
And I really like the TLR1 as a shotgun light, too (
http://www.copsplus.com/prodnum6043.php ). LEDs are great for shotguns- plenty bright, and they stand up to recoil better than incandescent bulbs.
Shop around for good prices and good service on any product you go looking to buy on the net, I posted the first links I ran across just for pictures and product info, not to suggest any particular vendor.
hth,
lpl