That "flare" looks pretty nice. I assume it's a flame retention cup, as per the Amal injector sheet?
There's lots of stuff on the interweb about "flares" in conjunction with homebuilt burners. I get the impression most of it is largely BS. The Amal injector has that nice coppery expansion section already built in and doesn't need, or benefit from, a flare.
The retention cup is very good at retaining the flame on the burner when it is used outside a forge. I also tend to use retention cups in dedicated Heat-Treating forges because the forge temperature is so low (around 800 degC) that the cup helps. For more "normal" forges (forging-to-welding temperatures), the forge works like a big flame retention cup and keeps the flame attached to the nozzle.
I mention this only because the retention cup is not an easy-to-find off-the-shelf part, AFAIK, and I'd hate anyone to be put off using an Amal injector as a result.