Hummm, well, I wasn't able to download the image or see what it was about. Thought it was a web page.....
Any way, if you're refering to some "selector" that replaces the plastic cover on the slide, then I've seen it. It allows select fire just like the Glock 18, but w/out making permenant mods on the slide. A while back, I ran accross some web page w/ a PDF file on a patent application on this. Select fire for a Glock by changing the cover to this switch. I thought it was cool too. Too bad I can't get one. Can't recall if I down loaded the PDF or not.
(EDIT)
www.fullautoglock.net Yup, that's what I was talking about. Not really bad price. Only problem is, if you own many Glocks, and Full auto, the weopon has to be registered. All can be made full auto.......talk about a situation. Ya can move this little thing to any Glock..... yikes, full auto G22 (or G35) w/ a Scherer stick mag.