I'll make a useless post and say I've never heard of them. Where did you pick it up from though? I would presume you have to stab them in the back though as that's where the pilots get into the PK's at.
May your terror missions always be infested with Chrysalids.
I picked one up at the Organization Storehouse in North Britain. It's just a big-ass sword. I tried it on the leader of the Unkown Complex with no luck, same with abandoned PKs. I seem to be able to destroy railings with it pretty efficiently.
It's called a Mechanical Saber,by the way. Scout PK only, 80-120 damage, crit bonus of 65. I can't target soldiers either, but when I targeted the fence next to him, it hit him and he exploded into bloody chunks.