I used to have them for many years on my primary bass. I stopped using them about 9-10 months ago, after the strap that had them on was stolen.
Pros:
They provide a sense of security and freedom of motion. I've never had a bass fall to the ground without them, but I've caught it mid-air quite a few times. So when I used them my mind was more at ease and I could concentrate on the music without worrying. Plus, they allow you to hold your bass at any angle you like. Also I Iike things that go 'click'.
Cons:
Minor: If you have basses without strap locks you are going to need a separate strap for them.
Major: The tight hold the have on the pin makes its screw go loose on the body a lot more often and faster, than when you are not using strap locks. So you have to check it and fix it often.
Your thread reminded me that I need to order a set again.