Small technical note-that's where it becomes brazing as opposed to soldering. 840f, I heard him say 8-something, close enough.
Top-end custom steel bicycle frames are made with brazed silver socket-type joints every day (most commonly 56%). Butted bronze joints bike, are fillet brazed as well. Brazing is serious metal joinery. Arc welding is a 19th-century joinery contraption.
Will work nearly anywhere in place of a weld.
I'd check on the solubility of that particular flux on the stuff in the video. All the coated rods i've used had non-soluble flux and you have to grind that away for cleanup. Nearly all the paste and powder fluxes will dissolve/soften in a water soak-the best joinery needs no shaping after that.
56% and Harris white flux is all you need to hang parts, besides clean metal and a small gap.