Recently we tested Airalo in Germany. Back then the service was provided by Ja! Mobil, which is now Hallo! Mobil.
As expected buying the data in the Airalo app is pretty straightforward. Buying it should be done at a WiFi Hotspot in advance. It does not make too big of a difference though as you need internet to activate the eSIM. To activate be careful to follow all steps provided in the description. We had some problems when we did not set the APN manually.
After getting the SIM to work the data speed is good. We didn’t notice any problems or slow-downs. Airalo promises LTE speeds, which we were not able to verify. One thing we did like was that you can easily top up your data volume without having to setup a new eSIM. Not committing to a big data volume we might not need makes the data used even cheaper than it already is.
Rating: 4/5 because we had to change the APN settings during the setup.