Forum user jamin had found Oticon Fitting LINK 3.0 available at a German web store. The BT dongle in the picture has a Sennheiser logo, which is not a surprise, as Sennheiser Communications is a joint venture of companies selling products under Sennheiser and Oticon brands. They seem to share for example their wind noise reduction algorithm.
A BT dongle looking similar to Fitting LINK 3.0 is sold as part of some Sennheiser BT4.0 kits, such as Presence serie headsets, available from various sellers for about $150 (UC or UC/ML). It could be and probably is only the looks that are the same, the dongle hardware or at least the firmware could be totally different. However, just because I am curious and persistent - has anyone tried to use such a Sennheiser dongle with Genie 2 to connect with Oticon Opn?
Just to be on the safe side, I must disclose that I have no experience with Genie 2 or any other fitting SW or HW. I recently got my Opns, would very much like to take these out somewhere in the more challenging environments, and do some tuning for my needs beyond what my audiologist can provide.