I know absolutely nothing about these, please be advised. I can't tell if the '8' and '4' are meant to indicate the designated speaker-size or the ohm rating of said speakers.
There is nothing to turn on or off - only an IEC cable that defaults to on when plugged in. You insert stereo 1/4" cables to the I/O's and that's about it.
I believe that these were built for professional PA systems or something of the like. The title sums up their purpose pretty well.
They seem to be a combination of limiters and passive filters with the purpose of filtering a signal before amplification.
They are line-level I/O -- do not place them after an amplified signal.
As noted, the MREQ 8 is not operating properly right now, but the other unit seems to be fine.
Combined, they aren't quite 1 rack unit, but they'll sit in a shelf pretty well.
IEC cables are not included.
Feel free to reach out with any questions - though, be advised that I might not have the answers.
Might be a cool project for a hobbyist or someone who genuinely knows what their application would be.