The thing you've got to understand about nylon, versus fitted leather or fitted Kydex, is that it is cheap. Generally, there will be no retention aside from gravity and/or retention devices like a flap, strap, or thumbsnap, and it is the sort of holster you cannot trust to retain your pistol. Worse is the fact that your pistol will move back and forth within the holster with every step you take, creating far more finish wear than would be created by drawing and re-holstering in a properly fitted holster.
Watch this:
Holster Talk Part 1
[YouTube]6id83qgQVic[/YouTube]
<http://www.youtube.com/watch?v=6id83qgQVic>
You are far better off buying a gun-specific, job-specific, properly fitted holster, in my opinion.