I'm having some problems with this as well.
The WiFi extender is FRITZ!WLAN Repeater 310
http://www.fritzbox.eu/en/products/FRIT ... /index.php
I don't think it has any options to create bridges or any such "advanced" options.
You only select the SSID you want to extend and set the security (enter the network key if WLAN is secured).
Here's the problem:
When connecting to the extender's WiFi, I get the hotspot's login page, but the next web page I try to open redirects me back to the hotspot's login page.
The problem seems to be that the WiFi extender is marked as an active client only for a second or two (sometimes a few more), but then gets removed from the active clients list.
I use the trial login option for the hotspot and the trial-uptime is set to 1h/1s.
I've tried making the extender's IP lease static
/ip dhcp-server lease
add address=10.1.1.2 always-broadcast=yes client-id=1:9c:c7:a6:7e:68:49 mac-address=9C:C7:A6:7E:68:49 server=dhcp1
and adding it to IP Bindings in hotspot's settings
/ip hotspot ip-binding
add address=10.1.1.2 comment="Fritz repeater 1" mac-address=9C:C7:A6:7E:68:49 server=hotspot1 to-address=10.1.1.2
but there is no difference if this is set or not.
Also, when a client (for example a smartphone) connects to the WLAN via the extender, there is only the extender's MAC address seen in the MAC table, not the client's.
Any ideas or tips would be welcome.