Another update: libsooshi’s example program and the more advanced sooshichef by the same developer work just fine, even without pairing with the Mooshimeter.

It appears the problem was in my head – I didn’t realize bluetooth devices could be used without some form of handshaking/pairing but apparently it works when done by the right interface.

In conclusion: Don’t try to pair with the Mooshimeter – you’re not supposed to need to do that. This is taken care of with GATT.