Tried it also earlier this year - very satisfying.

I tried mostly straight end mill 1/8" diameter (.125) - found out that I was able to cut easily with very low depth of cut - around 0.010" (.25mm) per pass at around 60 inches per minute. Depth of cut seems to be a very important factor for such small bits because it did easily break when trying to cut deeper.

I also tried Onsrud Super-O 1 flute up-cut bit of 1/4" diameter with good result at the same feed and speed as for the 1/8" end mill.

Note that I shoot air near the bit since everyone says that chip evacuation is important. I use an old HVLP air-gun turbine to push air and with this very low depth of cut, I get small aluminum shaving blown all around the work area. I used some baffles to keep the chips from reaching the CNC's rails.