Better speed through better CA (Carrier Aggregation). My test with Swisscom inOne Premium subscription in the ZH Oberland:
Speeds of approx. 80-120 Mbit at my home with the M1. Stable for months. With the M2 at the same location and the same antenna, speeds of 180-220 Mbit. Stable for months. When I take the M1, it's finito again at 120 Mbit.

The difference: the M1 aggregates to B3 or B20. While the M2 aggregates to B1 or B3. At least this is what my practical tests showed.

The web interface and app are identical.

My tip: recommendable as a DSL replacement with a good Swisscom Mobil subscription. But with a Swisscom subscription without the Speedbooster, 100Mbit is finito anyway. Sunrise never brought me over 70Mbit, no matter where I was. So take the M1.
By the way: the Akktu from the M1 does not work in the M2 although it looks identical. It even has the same performance values.

M2 supports more frequencies in the G4 range