I agree with above that longer barreled guns have better retention and this is true in any holster or carry style. Short snubbies or 'pocket' pistols are more prone to rolling out of the holster and therefore require firm or positive retention if they're not buried deep in the pocket. I shy away from positive retention straps or snaps and such and prefer friction. For example, my Galco ankle glove uses the "tension unit" rather than a strap. A holster with that would work well in the pocket but the holster would have to be positively retained to the pocket so it doesn't pull out.
Another thing I found is that short guns buried deep in the pocket increase the "pendulum effect." If I bury a steel J frame deep in my front pocket, its mass is down just above the center of my femur. When I walk or run, I have to swing that weight back and forth with every step -- it's almost as bad as a drop-leg holster. But with a long barrel gun, without extending the pocket depth, the barrel pushes the mass up higher on my hip. The limit to this is where my waist has to fold when sitting in a vehicle. This is one reason why long-barreled guns are better for pocket carry. With the grip sticking out, I can draw from seated. I just have to lift my hip to straighten it a bit. It's hard to draw when the whole gun is buried in the pocket and you're sitting. So if I was jogging, higher belt-line positions are probably better, or maybe a chest rig under a zippered hoodie. My point is, with below-the-waist pocket carry, there's some degree of pendulum effect. It's the only real drawback I see with below-the-belt pocket carry.
