"Old School" Indeed
I've a sample of a clamshell holster as well. I don't think mine is a Safety Speed, but it is the same design - and also for a 6" K frame. Sgt, yours is in excellent condition. (The history of police holsters is an interesting study in itself, actually.)
Rather quick, and even quicker if one's hand is already on the gun butt. However, that swivel feature will beat one half to death while running, and re-holstering requires both hands.
Drives the 'new' range people nuts, having one's finger in the trigger guard while still in the holster. [insert evil laugh here]