I carried a S&W 442 for many years to go along with my Beretta 92 first then my S&W 4506 as a great backup.
I carried it in my off side waistband, which you could barley see in a IWB holster. I could get to it with either hand and it was easy to draw while sitting in a vehicle!!
I always had a problem with ankle holsters. If they work for you then great but mine would always flop around when I was running and I found them uncomfortable. If you carry in an ankle rig you should have your draw down and practice with it.
I am surprised you are just realizing how valuable a backup can be. It was pounded into our heads at the academy as we were taught about the Onion Field incident and several others that occurred on my department. I carried a back up since I graduated the academy!!
Land of the Free Because of the Brave!
It is easier to be critical than correct and most people tend to take the easy way!