I have a Galco Fletch belt holster with retention strap, a Galco Padle Light with retention, a Galco Ankle Glove with retention for deep concealment, a Galco Belly Band for deep concealment, and a Desantis Nemisis Pocket Holster. All of these are used with either my 640 or my 340 M&P.
I like having options and I just made the switch to retention straps to aviod loosing my weapon during any physical contact.