FWIW I had my reservations about the "source first" licence grayjay uses as well, but I'm impressed by the FUTO org's principles, how they respond to bugs, how fast fixes and improvements come, amount of sponsoring other FOSS projects they do, etc. Plus Rossman's work for R2R and other generally good ethical behaviour. So I believe their reasoning when they say its necessary.
I ended up purchasing the licence and am happy with that decision. I just look at it as a donation to support the development, and the fight against big tech which would have happened if it was FOSS too in my case.
Also the best/only source available app to access nebula.tv content AFAIK ๐คทโโ๏ธ