Nothing? There is a differece between a unfused ground d-block and a fused power distribution. Example: Going 1/0 from batt. fused 18/20 inches from battery to rear to multiple fused distro then a d-bock with 1/0 in and 4 gauge out then to fused distro block to amps. That is usually the only time you will need a distro block. Going from a power source of one size to distro to one or more fused distribution blocks. I justed 1/0 to 4 guage as an example. It could be 4 guage to 8 guage. You can run straight to non-fused distro if you want but I do not like doing that nor recommend that to many ways to have an ooops. At that point you better hope the main fuse blows. I like the added protection. IMO
So the answer is no difference. Sometimes they color them different one has gold like plating and the other chrome looking. They are the same thing.