I am a fan of the RLS and have used it on my xd service for a few years now. I just bought a xds 45 and was curious if it was interchangable with the sight on the XDS. Success! I was able to reomve it from the xd service and install it on the xds. The smaller pistol is now my new EDC and I thought it deserved a laser that would work with the factory holster. i did not feel like the crimson trace would. Plus, i just dropped almost 600 on the xds and can't afford to have purchased another laser.
I really like the RLS for obvious reasons, I can use it with any holster. One tap of the thumb and its on and ready to go, can't get any better. I have used a rail mount but it always seemed to fly off eventually no matter how tight.
Its a little big for the xds vs the service ( more of an optical illusion thing) but I really like it. I touched up the white area with some GlowInc green paint to let it shine a bit, looks cool.