I bought a 500 Cruiser, shown on the right:
and it had this Insight tactical flashlight forearm.
When you switch it on with the small main switch, the pressure-sensitive grip switches have 3 modes: momentary on, on constantly, or strobe light.
It goes on and off the gun quite easily just by removing the barrel and one nut. ( circular thing shown in the 2nd photo.)
It seems to light up very well but personally I can't recommend it unless you have very large hands.
I have medium sized hands and I find the thing too large to grab and hang onto while I'm racking off the rounds.
The battery is well waterproofed by double o-rings & easy to change, and if you buy them in six-packs, only $2 each. (If you buy them at the wrong place you can get ripped off $12 for a 2 pack!)
The whole thing appears to be permanently glued together I cannot figure out how to take it apart and doesn't appear to be possible nor does it appear to be possible to ever change the lightbulb.
This is, however, an LED light, and so with the proper battery voltage the light should last longer than I do.
Still this is a $200 MSRP light, and I think it's a pitty that you can't change the bulb or the switches: two of the three things that always wear out.
This is the holiday sale ad from Impact Guns: