Get the Sure Fire Fore end and be done with it if your dictate a light on your shotgun.
Heavy yes, but the newer models are getting lighter and brighter. Some good deals can be found, but they are worth every penny. If you find a better solution, PLEASE post it. I have spent the cost of the SureFire over again looking for something "as good" cheaper and lighter. I finally broke down and got the purpose designed tool for my needs. Here are some things to consider:
1) Do you loose control of the light while racking the slide or when it is back?
2) Wires to get tangled up or caught on something?
3) Will the light stand up to the shotgun recoil (G2 will require a shock isolated bezel unless it is LED).
If you use the railed fore end, good luck.... Resist the urge to put a VFG on it, you will bend your rails eventually. Whatever you do, please train with it ....
Gratuitous picture