It has also been theorized that if you built one of these things and kept it fed (you have to add matter to it or else it would eventually evaporate in a BOOM) that you could use the power from on e device to start additional devices...
Basically it is just a Matter to Energy conversion engine that uses a trick of gravity to stay stable.
If you over feed it the amount of energy released actually goes DOWN... It is kinda paradoxical that way...
I’m sure just as we have mechanics to regulate the flow of gasoline into an internal combustion engine, some form of regulator would be needed to maintain whatever exotic physics needed to maintain this reaction.
Speed limit is 186,282 miles per second and no matter how much you feed this thing you’re only going to get to 99.999999% of light....in “normal” space anyway.