My understanding of using 56% silver for a filleted joint is that it can be prone to cracking. I have been told that silver slightly contracts on cooling and in a fillet it is the center that cools last, thus potentially beginning the joint's life with an internal crack.

Yet I have attached many (in my small production) seat stays to a lug's side with only 56% silver and have had good results. Or, at least, any bad ones had nothing to do with the filler... And I'd say that I've seen far more brass/bronze attached stays with issues then silvered ones (which should be the case as the number of silvered stay bikes is actually rather small compared to brass/bronze).

I've always thought that silver likes a large surface area to wet out on to (large as compared to the joint's parts and stresses), very clean prep and when right can be fast and very cleanly done with little later clean up. Great for lugs and thin wall located braze ons. LFB/brass is less cleanliness concerned, it's flux harder to soak off, handled larger gaps well (what fillets mostly are) and can cause distortion far more readily. Oh and it's cheaper to get.

That last bit is one reason why I began years ago to use LFB (GasFlux CO-4) as much as I could. Andy.