Dropped thigh holsters look cool and are theoretically faster than a belt holster. With that said, I wore one as part of a police tactical unit for years. That holster is designed to allow the user to wear high level external body armor.
The holster is a pain in the neck! If you walk, the holster and pistol migrate in circles around your leg. If you run, the combination gets in between your legs in a hurry. It is no faster than the converntional belt holster and pistol will bang against tables, vehicles, rocks, buildings, and get dirtier far faster. You can't sit down easily. The holster causes you pants to bunch up in the crotch area and you are always tugging at your trouser leg to get that leg down and your trouser waistband up.
If you wear external body armor, are using parachutes, rappelling, fast roping, or similar activites; by all means that holster is useful to a point. Uniformed patrol cops will not use these holsters because they just don't work for everyday activities. If you don't do these things on a regular basis while shooting, why have one?