However, the configuration is not easy. The (online) Manual does not help much further here. It is not just designed for the use of the repeater to a foreign base stations.
As described by the "Speedport-User", you can under the given address: enter the repeater Konfugurations menu "fritz.repeater" or [...] only when using a Fritzbox base station.
Even with my Linksys base station had assigned to the repeater a new IP. This one must first look in the Linksys menu and read. After entering the new IP in the browser you can then but easily access the AVM 300E menu.
The repeater need (after insertion in the socket) for the connection with the base station 3-4 minutes. Only then you should turn on the WLAN of the designated device.
Conclusion:
The repeater works as specified by AVM, also to foreign-based stations - but is a little "handmade" necessary.