I have one, It is a bit distracting for regular target practice until you get used to it. But it is pretty usefull for dry fire practice. It came in handy when I was teaching my son in law trigger control.
The Big Dawg's Club #1324
Thin to win - G36 Club #48
Kalashnikov Klub #1337
Kel-Tec Club #88
G-36, PF-9,P-3AT, Romanian WASR 10/63, Kimber 1911 TLE II Stainless