I used a SRAM RED eTAP road groupset with rim-brakes for about eight months and about 4600km. Here are my thoughts.
Changing down the gears resulted only in a rumbling clicking sound and sometimes, eventually a shift. I got the bike up on the stand and had a closer look.
After some playing around with the calculators I worked out that I can get something very close to my original compact 2x11 set up with a single, 44-tooth ring on the front and a wider 11-42 tooth cassette.
I'm planning my second Everesting, so thought that as well as climbing lots of hills to prepare my legs, I should do something to prepare my bike.