For fusion to occur, the hydrogen but be compressed at high temperature. If the hydrogen are slowed down to a metallic state, there is not energy for fusion to occur.

Maybe metallic hydrogen would allow for smaller H-bombs but that metal would still have to be energized at high temp.

The internet said so.

has potential as (chemical) rocket fuel

The paper's on arxiv, here.

https://arxiv.org/abs/1610.01634

It hasn't been reproduced, even by the original researchers. The original sample is still under pressure though, so experiments can be done. Some kind of phase change happened to get that last pic and nobody seems to be doubting the precursor black phase. The part that may not be appreciated is that the diamonds often break and it's entirely likely the next time they use the press they'll break it. So you can see the dilemma. Getting everyone's attention and input at this point was probably a good idea, even if it looks a little self serving.

The critics seem pretty skeptical in the Nature News piece:
http://www.nature.com/news/physicists-doubt-bold-report-of-met allic-hydrogen-1.21379