"but has a medicinal or tinny taste"
The first sounds like a good equipment cleaning would help. The second "plenty of gas ..but is very cloudy indeed
and taste is bloody awful - sweet and i think alcohol free" sounds like ferment never finished or even started. Perhaps a good shake up after the heat band was applied would have helped. It may have been expired yeast as well. My experience with the canned malt is the yeast has usually been close to expiration or well past it. Plenty of gas was maybe from the c02 injector? BTW, how are those beerspheres? Is there a good seal always, or does it leak? I used to have a king keg years ago, and the valve always leaked.
Anyhow, take a deep breath, try again. Everything must be cleaned well, and give it another shot.