I'm not too familiar with the Power Lock...

First: Is this a Power Lock or a Detriot:

http://abacus.sj.ipixmedia.com/abc/M28/3dbc478ea5c2ae2c572ea5d3f/i-1.JPG

http://abacus.sj.ipixmedia.com/abc/M28/3dbc478ea5c2ae2c572ea5d3f/i-2.JPG

Second: How is it different from a Detroit? Is it a true locker, or a clutch driven type of posi?

I've got both
Detroit in front- power lock in rear

Power lock works like a posi . It works nicely
I haven't had any issues with it. It locks well when needed.

I will eventually change the rear to detroit when I upgrade the rear diff

that is a pwr lock and it is a clutch type limited slip

What's it worth?

It's a 35 spline for a Dana 60 4.10 gear set.