I just got a NexTool / TaoTool keyring package opener from E-bay
The blade is supposed to be teflon coated, so sticky stuff (like packing tape glue) is easier to clean off. The blade is also reported to be made from Swedish Sandvik’s 12C27 steel.
The tool is longer than a regular key, and opens like a regular penknife blade.
You can see the backspring flexing as I open it. This is the version with a stainless steel body. I've seen versions with colourful plastic bodies.
It works, and the hooked blade is fairly sharp. The blade locks into position, and needs to be released before it will close ===> iirc, not legal carry in the UK
There is also a second curved long cutting edge, which is not as sharp as the hooked part. There seem to be two thin brass washers either side of the pivot/rivet the blade rotates around.
All in all, it's solidly made, good solid movement, and nice click when locked into place. No noticeable flexing anywhere.
I might dis-assemble (break) it and use the blade in another tool.