The stuff to look for in ANY holster would be:
1) How it fits the gun. You want it to retain it well so it doesn't slide out, but you also want the gun to come out without too much of a yank in the event it is needed.
2) Comfort. How the holster distributes the weight is a huge part of this, as is the position of the gun in the holster (once attached to the belt).
A paddle holster is one that is generally OWB (outside the waistband), and can be taken on and off without removing the belt. The paddle conforms to your body, so it is reasonably comfortable, but for larger guns, in my experience, paddles just don't conceal well. Yes, you can throw a long shirt over it, but the bulge is extremely conspicuous. A belt slide holster will hold the gun tighter in (reducing the bulge), but at the cost of some comfort and lesser ease of removal.
IMO, I use inexpensive paddle or belt slide holsters (when it comes to larger guns) only until I can get a good quality holster (not cheap, not quick) made for me. After that, I use the paddles for things like when I am working outdoors. They have their place, but for service-sized automatics, they aren't the best for concealment.