Hello, first post here :D
A few month ago I modded a FW1AA with boost-buck driver for NiMH/li-ion and with RGB LEDs.
I used a TIR lens for the aux led to shine through, unfortunately it had artefacts in the spill that ended up a bit too distracting so I went back to the original reflector and used a thin flex PCB under the reflector with tiny LEDs that fit in the opening. I’m very satisfied with the result, plus the beam with the 519A+ SMO reflector is surprisingly good.
Edit : putting the video in the text since it didn’t create a YouTube thumbnail : https://youtu.be/u6aYa8FEt3s
I don’t remember exactly but I probably chose the 0.69mm ones because they cost half as much. The 0.04mm difference being pretty negligible. I also have the 0.9mm ones that I use when the classic 0606 are just a bit too big, they are easier to handle.