My thoughts on holsters for concealed carry will mostly depend on your dress code.
Any holster can serve as a Conceal Carry providing you wear a long coat or shirt with the tail out.
The IWB holsters are intended to be worn inside the pants and hang on a belt.
There are Tuckable IWB holsters that allow you to tuck in your shirt (even a T-shirt) between the clip (and flap if attached to a matching flap) and the holster/gun. I suspect these are more common in warmer weather where T-shirts or Polo's are worn and the person wants to tuck in their shirt tail.
My carry weapon will be a S&W M&P .40 full size. When I start carrying I will likely have 2 holsters. I like the Bianchi Sof-Tuck for warmer weather which is as I described lastly above and something like this Bianchi II Shadow 7 for OWB belt holster but also concealed carry - with a long shirt or coat.
IWB for concealed carry warm weather - DeSantis Sof-tuck
OWB for concealed carry cooler weather with long shirt or jacket/coat - Bianchi II Shadow 7
Bunch of mfg links for holsters: