To answer the original question, a harpoon in a PSK...

Silly. The thought of adding it is just plain silly. The chance for the average internet joe to use one successfully is nil. Those that have the skills to successfully use one could make and improvise IMO.

And yet there will be droves of folks buying them at $80 a pop to go with their $300 pocket knives while complaining how expensive ACR PLB are.