I have two brief observations on this often discussed topic:
1) If you happen to see a gun someone else is wearing being exposed in an apparently accidental manner, if it's in a holster, he / she is very likely a good guy / gal of one type or another (LEO, CHL, etc.). If it's not, there's about a 95% chance you're looking at a bad guy.
Reason: Good guys carry guns in holsters because that carry method is more comfortable and secure. Bad guys carry without holsters because they want to be able to ditch the gun without any indication that they had been carrying one. Cops know this. It's a fairly reliable rule of thumb.
Yes, I know some cops and CHL holders carry without a holster. Such folks have a much higher tolerance for unnecessary risk than I do. Other than for LEO's who have to carry this way to fit their undercover roles, I think holsterless carry is a really bad idea. Besides being uncomfortable and insecure, it carries the unwritten presumption of bad guy until proven otherwise in the eyes of any LEO you may encounter. This can most certainly affect interactions with LEO's if that manner of carry is observed.
2) Abbreviated
"slide style" holsters that use the smallest possible amount of material to hold the gun in place and leave some or all of the barrel exposed carry an increased risk of unintended exposure. If the covering garment rides up a bit, what's exposed is clearly a gun instead of just holster material which could be part of a belt rig for tools, phones, or any number of things. Around the ranch it's fine, but I think it's a bad idea out in public where it reduces the margin for error. Although they're comfortable and inexpensive, I don't own any for that reason.