Hello Pascual3, I have had this device for a while and have already operated it successfully and without problems with three different Swiss mobile phone providers (Yallo, Sunrise and Swisscom) as well as foreign providers (e.g. in Italy with Vodafone). Because of Media Stream, it works exactly as described by the manufacturer: Insert a micro SD next to the battery compartment or connect a USB hard disk or USB stick via the USB port and your router becomes a streaming server. Pictures and videos can then be played via browser, app or VLC, for example.

Hello
Speed fluctuations are normal in the mobile network.
I can test whether you can use a USB hard disk on the M1. However, I would advise against this. Streaming media is not possible from any router. Only access to the files is possible. To use your own film collection on several devices, you should use a NAS or a server with Plex.