I recently purchased an XDM 4.5 in bi-tone (9mm). I also purchased the Viridian SXD laser sight for it. The green works quite well in the daylight, where the 'red' may not. The SXD mounts quite firmly on the rail, easy to install and remove. I have not had to adjust the sight after remounting. I found the Viridian SXD on line for under $200 with a free pistol case and a free holster that fits the XDM with the laser sight attached. Other than looking cool on the XDM I'm still not sure if its a "have to have" attachment. The green light did look cool at the indoor range the other day after the lane got a little 'smoked up'.