Drop leg holsters aren't great for distance travel. They also catch on everything, and the straps cramp "the boys".

I've used a Safariland 6004 in classes that required a secondary, and it is probably the best of the breed. You can position the holster as close to the belt line as your ruck or belt order allows, but its still a drop leg.

For "bugging out" I'd consider the excellent M12 issue holster. The M12 is slow on the draw, but protects the firearm and is bomb-proof. It will clip to virtually anything, and can be adapted to MOLLE use if desired.