When I was first hired as an LEO, we were issued Don Hume Jordan holsters with the safety strap. Later, we transitioned to Safariland 229, a mid-rise thumb break. The thumb break, or any other kind of retention device, is not to prevent a gun grab, but to hold the gun in the holster as you are moving around, i.e., getting in and out of a patrol car, bending over to pick up something, etc.
Today, when I working around my ranch, I have a holster with either a strap or thumb break, depending on what gun I'm carrying. Again, just to keep from loosing the gun. Most of my CCW is pocket or IWB carry with a J-frame, so I'm not as concerned about retention as I'm not doing the things that would cause the gun to come out of the holster unexpectedly.