You should be able to use any router as repeater regardless whether it uses our firmware or not.
However, make sure the following configuration is done on the repeater:
- No dhcp server
- No firewall
- All interfaces, WAN, LAN, WLAN must be bridged to LAN
- The repeater must have an IP address on LAN in the 192.168.12.x range with x any value other than 1
- The repeater must have set as gateway 192.168.12.1 in its network definition
- The repeaters must be set to a fixed channel (not auto) and of course it must be the same
And then depending on how your router's firmware does WDS linking (lazy or discrete WDS) you must set either to same SSID or link to each other's MAC address.
On the repeated main router you must also activate WDS in the network definition of the wireless network you wish to repeat.
If you feel confident to achieve the above, then fine. If not, then you may be better off to use router that uses our ChilliWRT firmware and is configured to connect via WLAN to another ChilliWRT router. A guide to achieve that is HERE