What Goldenlight said. IMO, the guns are built like tanks. I have experience with the 645, and 6906, and some with the M59. Good guns. I carried Glocks on duty for long time, but always liked the S&W's. The first 6906 I had was an early generation, and had stoppages traced to a weak extractor spring. Then it broke the trigger drawbar. Lost patience with it and sold it after repairs. After retirement, I bought another 6906 of third gen. persuasion. It has been great. Don't recall ever having a stoppage with this one. I had a friend that had a M59. He used to fan fire it, dumping a 15 round mag as fast as he could work the trigger. The slide would lock back, the smoke poured out of it, etc. Neat to see, but useless as a technique. But the gun never jammed.
If I wanted a super concealable one, I'd probably take a look at one of the 3900 series guns. They are thin in the grip and don't print quite as easily.
The Glocks are good, but when wearing one close to the body, such as under a sweatshirt, etc., I am a little leary due to lack of an affirmative manual safety. Don't have that worry with the 6906. I can apply the safety, reholster, and then take the safety off. I know the Glock is safe, just my own preference. There was a football player in NYC in a bar, if I recall correctly, who shot himself in the leg...Yup, it was with a Glock, just stuck in his waistband, and something fouled the trigger.
If you can find a clean Model 5906, you will have you a good, solid, shoot'n iron. There are, as you know, more modern systems out there, but the 59's can still do good work. Just my .04 worth <tax included>