The bi-metal (Silver/nickel) was very popular some years back (20-25?) to keep costs down. Be glad IJS will sell it in 4.5 x 18! We had to either take a full mill run or a minimum of 6 x 36! It does work well when you need something stiffer compared to the other silver alloys available. Costs about 60% of sterling, but you only get 20% precious metal... and cannot stamp anything made of it "Sterling".
Sterling is our standard for fabrication. Been working in that metal for 45 years...
.999 sheet and wire is used in our enameled products.
Personally not fond of Argentium, because the solder made to color match it melts to the consistency of peanut butter and has to be pushed around the joint with a pick. Does not flow well.
Using standard silver solder you'll eventually have a dark line against the Argentium. Also once dropped a large hot piece on the floor one day. Shattered like a piece of glass... something that has never happened with other metals we work. Only used by special order for those reasons.