Similar setup on our Co-Motion Speedster tandem. 28/42 front rings on a road triple crank (74/130 BCD), with an 11-speed 11-40 cassette (we live in Switzerland). Rear derailleur is the GRX Di2 11-speed, and I believe the front der' is Ultegra (because the GRX FD is made for a wider chainline). It works perfectly and we're very happy with it. Multiple junction boxes means that it's easy to unplug when splitting the bike for transport.

I'm not a fan of SRAM in terms of ergonomics of the hoods, the fact that you need two hands for front shifts, keeping an eye on the charge level of 4 batteries instead of 1, and many other aspects of their design, engineering, etc.; other people don't seem to consider these to be drawbacks.