No matter what sort of work you do, at some point you end up needing a sharp edge. I usually have a small folding knife with me for just such occasions. Sometimes, other people need the sharp edge so I lend them my knife. Now, they can open it fore sure, but almost everyone is confused on how to close the knife.
I even had one co-worker who ended up disassembling my knife trying to figure out how to close the darn thing!
It’s just a skill people seem to not have and they should as it’s a very popular design.
I have included a link to a video which illustrates how to close a knife. The video is not mine.
Liner lock knives have been around for decades, I think that suggests there isn’t a problem when used correctly. The benefit is that you get a very secure folding knife when the knife is extended, and you can fold it with one hand.
It does indeed seem a little safer when extended, but I feel that the danger of closing it far outweighs the additional safety during use, regardless of technique used.
Furthermore, and perhaps more as a side note: Even if something is decades old, does not necessarily mean that it was safe or wasn’t riddled with problems, but it does imply that the tool was at least usable when handled correctly. As much as I love them, I think helicopters in general are a fine example of this.