"Plugged" my 340PD and tossed the parts and key. Never gave it another thought until I saw this thread.
I guess I really have no opinion of the lock on mine because its the only s&w that I've owned (so far),
Note that if you ever need to have S&W work on the gun under warranty claim, it needs to go back to them with ILS installed. Therefore, best to hang onto the parts or even pass them along in any sale.
This may or may not be true. I called S&W CS they said each gun is evaluated on an individual basis. I asked if a gun with the IL removed would still be covered by the warranty. He said most likely yes. He said any modification would void the warranty. Even spring replacement. He was very vague about giving a definitive answer. He said that if a gun came in really buggered up by the owner; it wouldn't be covered. If a gun came in relatively clean without the IL it would be covered.
I only have one with a lock. Its a four inch N Frame that is rarely carried. I'm sixty and there are no children in my home. There are no grandchildren yet. My guns stay in a safe unless I'm using them. So, I just ignore the lock. If I was a guest in a home that had or might have children in it and I had to remove my gun and put it somwhere out of my immediate control, I would use the lock. I can think of a couple other improbable situations when I might use it. So, I don't use it. It doesn't bother me and the revolver that has it, has one of the best DA trigger actions I have ever tried so the lock doesn't matter to me.