I have the one they sold for the Valkerie. At the time I got mine, they'd just gone out of production. The whole system with the antenna (usually extra) set me back about $700. I've been pleased with mine since I put it on the FJR in 2003. External audio for MP3 or Sirius radio, intercom (which I don't use), and CB. The Valk unit was designed as an add-on system, so many of the leads may be longer than one ripped out of a Gold Wing. See if it's from a Wing or if it's one of those sold for the Valk. You can see photos of mine at: https://www.fjr-tips.org/acc/cb/cb.html
Can you test it before buying it? Buying used electronics can be good or bad. If you consider it, ask if they will provide you with a guarantee of servicability (especially if they don't let you test it before buying it).
Some have failed because of improper installation (no drip loops on the wires and water crawled up the lines into the control box). Long term, support is excellent though Sierra Electronics. They do flat rate repairs and you get a component-level repair if ever needed.
I have the exact same setup as above. Works great and fits the FJR quite well. I got luck and found one for $100. Plus I had to buy a headset and antenna. Worth it if you can find one but I wouldn't pay over $300 for one because you can get a J&M setup for that price range new. www.jmcorp.com