Well if you follow what happened with the 780 ROM it turns out all Mac ROMs past the 680 are made by him anyway so I guess it doesn't matter who you buy it from. I don't recommend those other people for other reasons such as the fact they are selling something that isn't theirs. It may not be illegal but it's not fair to the modder who put the ROMs out there.
The others are flashing same rom on all cards. As a result, fans are noisy, card is overheating, performance is horrible, specific ports are not working. In the worst case it's going to produce a brick and there is no magic BIOS switch on GTX cards to bring the original rom. Such cards will require soldering and chip transplant.
This is one of the victims: https://forums.macrumors.com/thread...rd-list-finally.2124795/page-17#post-26287231