Hi Kenbar, I bought the large because I figured it would hold the light better but I'm not for sure as I haven't seen the smaller one. The large kydex holster is very secure and has a Tek Lok for securing to your belt, etc; You can leave the light clip on or off as it doesn't matter.
In my view, the holster is the best method for carrying the light edc. Is it worth $50, actually mine cost $39 from Jimsflashlights.com and it was worth every penny. I know the guy who actually makes them, David Brown, and he also makes kydex gun & knife holsters and he is very, very good at his craft.
These HDS lights really do amaze me, I will be going another one very soon.