Ben Weisswrote a review of SRAM Red eTap AXS Front Derailleur on June 14, 2019
Familiarity: I've put it through the wringer
I have a SRAM AXS groupset on my new Canyon Endurace. After about 500 miles, my front derailleur is refusing to shift. I tried everything - firmware upgrades, pairing, reassigning buttons, hard reset - but nothing solved it. I'm in the midst of getting a replacement from SRAM (20 days into the process and no derailleur yet).
I looked at two options for my Canyon Endurace - SRAM AXS and DuraAce Di2. I figured wireless was the way to go. But I did not anticipate electronic problems.
Here's a quick comparison of Di2 vs. AXS (I have a Di2 groupset on my BMC GranFondo):
1) Shifting buttons: SRAM - single button is very intuitive (press both to toggle front derailleur) and if your hands go numb like mine, it's easy to mistakenly press the small button on Di2.
2) Shifting: Di2 - definitely faster and I like how the front derailleur will automatically adjust to rear derailluer shifts.
3) Gear ratios: SRAM - I've got a 10-33 cassette with a 35/48 front, giving me more high-end and low-end than my old Di2.
4) integration with Garmin: Di2 - The SRAM battery field show as 5 bars (not a percentage) and I think it shows the battery with more charge (usually the front), so the field is fairly useless. Also, the Garmin does not support a 12 speed in the gear indicator.
5) Rear derailleur adjustment while riding: Di2 is easier to enable and shows up on my Garmin, along with the +/- micro-adjust setting. With SRAM you have to see if LED is on when you press a small button on the lever, which is almost impossible to see while riding.
6) Batteries: SRAM - it's nice to have a battery you can take off the bike. It's also nice to be able to swap front and back batteries (they are identical) if the rear derailleur runs out of gas on a ride.
7) Looks: SRAM - hard to compete with no wires and no control box below the bars.
8) Reliability: Di2 - I have over 12,000 miles on my Di2 bike and not a single problem. My SRAM front derailleur stopped shifting after 500 miles.
As you can see, there isn't a clear winner, but if I had a do-over, I would change to Di2. The reliability alone is worth it.