When I ordered the stuff I bought it in the cheapest form I could, raw cast plate that had been rolled down to 5mm, and that's worked out great. Of course you need a rolling mill to make good use out of it in that form but the stuff is a joy to roll. It work hardens noticeably slower that regular sterling and if you're careful you can pretty much avoid pickling after you've annealed.
Did you ever use the hardenable silver that Johnson Matthey used to
sell in the 80s? I wonder how these new alloys compare?