Do not bother with the product, it performs poorly with common aluminium. Even with a sandblast surface, cleaned there's no capillary action at all. The melted alloy would just balled and wouldn't even wet even in a control oven.
Interesting ... I need to braze/solder aluminum soda/beer cans one on top of each other ... no one seems to have done that in recent years ... they did years ago with steel cans and solder ...
If you’re still looking, try Casweld Europe. Their Pot Metal Solder kit is exactly the same stuff. No idea how they’re getting away with it & it’s not cheap, but I’ve found it works well. I needed to repair a piece I thought was aluminium but it turned out to be zinc (or at least zinc based). I made an aluminium replacement part & used this to join the two. It’s worked well.
Soak the piece in hot water (from a boiling kettle). Leave for a while then brush it off under running water with a wire brush. That flux will come right off.
