Most of the similar Prodelin or CM dishes I have found have had the very same feed horn and LNB attached. They are for receiving a single transponder on one satellite. DTN, Musak, and Music Choice would likely have sold these as a package with the receiver.
I usually get them for free, that's quite pricey for a used one, guessing that would be close to a new unit price when it was originally purchased. It would be very expensive to ship though. You can usually find them on (smaller) office building roofs, gas stations, restaurants, radio stations (TV too), and numerous other businesses have used them. Many of those services have gone to IP delivery so often these are left on the roof unused.
If you get it, keep the feedhorn. It works best for that dish and you can use an Inverto LNB that bolts right on giving you both polarities.