The K3U is a power module that you put various heads on.
I have one with ME80 (shotgun) and ME20 (omni) heads.
The other head I know of is the ME40 (cardioid).

The local theatre group has about 8 of the ME80 shotguns. They work well but I find them a little noisey. Could just be their age though.

Interestion point to note is that the K3U take a battery as well as 48v

Oh, I should mention that I use mine with the ME20 as a talkback mic.

Kinda shows what I think of it as a recording mic ;)