Any other recommendations for mobile Wifi router which I can use for on the go. Where I can simply insert a mobile data SIM-card for using it while I'm outdoor?
(I want to use it as a simple internet access for my rasperry pi 3 - if it works)
The firmware that drives the 4G radio is always closed-source. Most of the "MiFi" or "Pocket Wi-Fi" devices such as that one contain only one CPU, with integrated 4G, routing, and Wi-Fi all in one closed source firmware. They can be used with a box running OpenWrt by wifi or USB tethering them. Since you don't need the battery power or integral Wi-Fi features, you could use a simple USB modem dongle on a Pi3.
@lleachii thanks!
I'll check the devices and if I can buy one on amazon or the official device website. Will text you if I have other questions about details thanks
@reinerotto
Your name is german so I write german now .
Kann man der Firma vertrauen? - verkaufen fertige Router mit OpenWRT. Kenne mich nicht so gut aus aber die Website sieht nicht so seriƶs aus?