I did think it might be one of the few exceptions. AFAIK his lens (in it's two guises) is one of two AF mirror lens produced, though one of mine can be used with the Techart pro to gain AF finishing. There was also apparently a mirror lens with adjustable aperture made, though I know even less about that model.
My Samyang 300mm/6.3 mirror is designed for APSC & MFT so manages at 600 equivalent (on MFT) & only weighs 320g (& 7.5cm long) but admittedly it doesn't have AF..
I've also tried 500, 600 & 1000mm mirror lenses with MFT as well as the Pentax Q for even more reach though they are FF models. Camera shake was unsurprisingly a major issue with the Q (crop factor a little over 5) but on a reasonable tripod & with good light the MTO 1000 on MFT (2000mm equivalent) worked OK as long as the subject was static enough to allow careful focusing. I don't remember getting anything remotely usable with the Q, but I tried it in poor light without a decent tripod so that's hardly surprising.
The MTO weighs over 2.4kg so is very much an exception to mirror lenses being light weight. It's made worse by coming with 3 heavy filters that screw on the front (most mirror lenses use filters at the back)
I wouldn't mind adding the Minolta 500mm reflex lens to my collection, but now I'm retired I can't afford £100 and my A to E AF adapter could do with an upgrade...
To bring things back closer to theme
@Adhd.Artwork have you had a chance to play with it yet? Can you share any pics