I have the Quik-2-See by Anderson Flashlight Systems. I got a kit online for 14 bucks. It has 2 base plates and one flashlight attachment.
I found that it only works on FML mags. The base plate would not stay onto a NFML mag. The base plate must be a very good fit if you want it to stay on. Luckily, I had a preban FML that the plates fit well.
The Glock is so light to begin with that the extra weight of the flashlight (4.4 oz) doesn't really bother me. The Quik-2-See itself is made from aluminum and only adds a couple oz. The Glock + Quik-2-See still weighs less than a 1911.
The systems seems to work well. Since the extra weight is at the bottom of the grip, balance doesn't seem affected for me. It just so happened that the range was having some electrical work done the day I was trying it out. All of the sudden, all the lights at the rear of the range went out. The Quik-2-See + Streamlight Scorpion did a great job of illuminating the target 50 ft away.
I think that this system has great value. The Scorpion is bright enough to illuminate a target 50 ft away, and to momentary blind a person 20 ft away. That, along with being able to clearly identify what you're shooting at, makes it worth it for me. All I need now is guide-rod laser and it would be perfect!
These guys have them for 12 bucks on closeout. For that much it's work trying out.
http://www.hunting-camping.com
Go to Product lines ->Hunting Shooting. Then find QUIK2SEE