While I don't have any S & W with the internal lock, I do have several Taurus with a similiar system, and have not had any problems with it. I did play with it when I first purchased them, I haven't used the lock since then, but they have never failed to go bang, except for ammunition issues.
Many people may have legitimate reasons for not liking them, but for the people, that for whatever reason, want/need them, what do they hurt?

Brian