Beyond concealment, a holster has to have three equally important main attributes to be really great.
SAFETY
Does it cover the trigger guard? This is a no brainer.
Does it allow a proper grip on the gun? You don't want to have to change your grip once you get the gun out of the holster. That's valuable time you should be using to acquire your target.
Does it offer a clean presentation so the muzzle doesn't cross the body? You should never point your gun at anything you don't want to shoot. So why allow the muzzle to cross your body when you draw?
Does it keep the gun secure in the holster during normal activities? A weapon that doesn't stay where it's supposed to is useless.
ACCESSIBILITY
Can you quickly get to the gun? Time is of the essence.
Can you effectively get to the gun? Even if you can get to your gun quickly, you need to be able to get it out easily.
Can you draw with one hand? Can we suffice it to say that this just makes sense and not take up the time to go over it?
COMFORT
Can you sit comfortably for periods of time if necessary? If you sit in a car or at a desk a lot, you'll want to make sure that the holster you select is comfortable enough to last throughout the day.
Keep in mind - some have said that a concealed weapon should be comforting, not comfortable. This makes a cute saying, but ignoresthe fact that most people won't wear a rig that isn't comfortable.
