Bridge mode is when eci modem working purely as modem and your username and password came from router to modem for connection authentication.
This fw is maybe old but is nothing wrong with it, vdsl fw support g.inp where possible, and other types of connection. This fw is dedicated to use in UK as there are pre set wan bridges. I tried newer version 18.06 and also on different modem I tried 19.07, apart of newer kernel and fresh packages in 19.07 there is no more futures than in this fw. If you will use this modem in bridge mode all firewall stuff will be done by your router so there is no big issues if some packages are outdated (in my opinion). Also bear in mind that this particular fw was tweaked for use on eci modem and is really damn stable. If you planing to use eci bt modem this is the best way for it. Of course you can try newest Openwrt but you will came back to this one at the end as I did. Don't buy bulk quantity, get one eci modem flash this fw and see yourself if it suit you.