Choosing the RIGHT holster will often make the difference between carrying your firearm concealed or leaving it in the vehicle or at home when you go somewhere. If the holster is uncomfortable, too wide, too loose fitting or does not allow easy draw chances are you will choose not to carry your weapon. A good holster will ride comfortably, be low profile, fit snug to the waist for OWB, be comfortable carrying IWB and allows for a smooth draw. People who have comfortable holsters will rarely be without their CCW.
As far as Uncle Mike's holsters go, I do use the Sidekick #16 with retention strap for my C9, but its a field carry only holster and it rides in my GHB just incase I need to holster carry the C9. UM Sidekick holsters are just too wide to be good concealed carry holsters, and they also tend to flop around on the waist when you are active. The only way I could CC the C9 in the UM #16 holster is if I were wearing a Parka or Poncho, otherwise it sticks out like a sore thumb.
I also tried three Uncle Mike's Super Belt Slides with thumb break on my C9, Makarov and Bersa Thunder. I was not pleased with any of these holsters because they would loosen up on the belt and printed badly. I tried one of the UM SBS's with my S&W 9VE and it had a horrible print. I have since bought Fobus Paddle holsters for my Makarov, Bersa Thunder and S&W 9VE and they blew my mind at how comfortable they are and how little they print as compared to the UM SBS's. The next holster I buy will be a Fobus Paddle for my C9, then the UM #16 will be put away for good.
Second most important thing you can get, besides a good holster, is a good quality sturdy belt, especially if you intend to carry OWB. Even with an IWB carry you want a quality belt because it makes for a more comfortable carry when the belt does not sag under the weight of your CCW. A sturdy belt will also aid in making a smooth and clean draw of the weapon from the holster without giving yourself a wedgie.
Last thing to consider when carrying a firearm is clothing choices. If going with an IWB you will need to get pants that are at least one size larger than what you normally wear. If carrying OWB you will need shirts that are at least one size larger than normal. The larger clothing makes packing the gun more comfortable or just easier to conceal without major printing issues.