I have been using it with my XT11 for almost 3 months now. It has never fallen out for me yet but I am conscious about the possibility and check it often. I like the easy deployment. The only thing I can complain about is that I wear it on the rearward side of my waist and sometimes I have to manually adjust the angle of how it sits on my belt when I am driving so it doesn't dig into my back. If you wear it more to the side, it isn't as much of an issue I guess.
I also found a more heavy duty lockable holder here:
http://www.phoebustactical.com/Rotating-Fast-Holster-14-p/prfh-14.htm
Looks like it should work. If anyone has tried it or knows about it, please let us know how it works!