The upside down knife may or may not look cool - I really have no idea. I encountered this technique in cave diving, where you fairly regularly encounter situations where you really need a knife, and quickly. Drawing with either hand is a worthwhile advantage.

You are certainly correct about more easily losing the knife in this position. I would rather attach the knife to the waist belt of the pack, or just keep it in the pack. Another option is to simply slip a SAK into your pocket. It will do 99.9% of what the larger, more bulky blade will accomplish.

In a lot of situations, off trail in dense brush or in technical climbing situations, a slim uncluttered profile is a most important consideration. I can't ever recall a situation where I really needed the quick draw capability of the upside down mount. But if the QD is what you want, attach it handle down.