Pros and cons:
Pocket holster, pro:
- can access weapon by putting hand in pocket, so preparation for action doesn't look like threatening/brandishing;
- works with hiking shorts and tank tops;
Pocket holster, con:
- can make it a challenge to figure out where to put car keys, pocket knife, and wallet;
- hard to access from seated position;
- must must must remember not to put anything in pocket that might get into holster and catch on trigger (IE do not put anything else in that pocket)
- doesn't work well with anything larger than a J-Frame for most people;
- only works with relatively roomy pockets (IE not Levi's 501's)
I have a DeSantis Nemesis pocket holster for my PM9, and it tends to get used when I'm in super casual mode (shorts and tank or t-shirt). Otherwise, I prefer IWB for most purposes, and OWB for great outdoors/open carry use.
IWB, pro:
- can conceal anything up to and including a 4" .44mag (I do every so often)
- pants and belt both help hold the holster in position;
- tends to snug the pistol grip tighter into the body than does an OWB rig;
- can be adjusted for reliable access from seated position, including in car
IWB, con:
- may need to get pants one waist size bigger, depending on how much slack you have now;
- if you don't wear an undershirt, you will have pistol up against your skin (even with a bodyshield on the holster, some parts will probably rub);
- pistol is exposed to more of your perspiration, which may accelerate corrosion;
- outer cover garment (shirt, sweatshirt, jacket, etc) required for full concealment