Early in my carear, off duty, I used "Mexican Carry". Once the GW Davis and Milt Sparks IWB Summer Special holsters came out I have used them 100%.
I am wearing one now...

They are unique in that you can "open up" the top of the holster for a faster draw, or "pinch it down" for greater retention.

For duty use I always used a thumb break holster, whether carrying a 44 Mag S&W, a 1911, a S&W 45 ACP revolver, or a Glock 17.

I always carried the holster unsnapped....

I knew when I was about to have to "fight" a suspect, and always had time to snap the thumb break...

Or when I was about to do some "aerobatic stuff"...

When making entries, carrying a long gun of some kind, both of my handgusn were snapped in... See "aerobatic stuff" above...

I still always practiced my draw with the holster snapped...

I learned this system from Bill Jordan, personally...

Always worked for me.

When in the field I use a thumb snap holster and keep the snap fastened.