anyone know anything about these guys? how do they work? are they worth picking up?

i have one my dad gave me years ago that's been sitting around in my closet for a decade. when i was a kid i would tinker with the thing for hours, hooking it up to my dad's Akai reel-to-teel. in theory, i think it's supposed to turn an ordinary 2-track into a tape echo as well as allow you to supposedly do overdubs somehow.

i never got it to work.
the manual confounded me to no end.
but then again, i was a kid and could barely understand anything much more elaborate than my yamaha cassette 4-track.

hmmm, perhaps i should look for the thing and try again.
(now that i am older and only slightly wiser.)