We had the same experience as DankyOne in a hotel in Vienna- used the safe, then couldn't get it unlocked. Had to wait for a manager the next AM to use some sort of passkey. Fortunately, we didn't need anything in it urgently.

Now we use the free ones, but only after testing it. I'm a jewelry freak but decided the most practical course is to bring one set of jewelry and wear it all the time. Then I don't have to worry about stashing the spares. In Brazil, we had an in-room safe but when I bought a bracelet at H. Stern I was too paranoid to use even that- I hid the bag and also hid the bracelet in a dirty sock till we got home.