tried it today and loved it. gave me lots more flexibility with heating. i did overheat one part trying to bring the filler down with the flame, but i felt the difference between "filler filling" and "cooked like a biscuit" was far greater. even the part that i cooked had decent penetration.
i had expected more trouble getting the flux off afterwards than with white flux, but it wasn't noticeably harder.
this was another split-tube practice joint, which isn't really the best way to practice i think; sometimes the gap isn't very even so the silver won't flow evenly. i'm gonna try a bottom bracket shell this weekend.
i took these right after i turned off the torch. the metal was still hot enough to need holding with pliers.
here you can see the part i mentioned that i had cooked. after clean-up with hot water, this black spot was still mostly there. other than that blotch, the joint cleaned up to about what it looked like pre-braze.
i'm awful proud of that line of silver all the way round the edges.