Teltonika RUTX50 as router on Openreach based FTTP?

I migrated from Zen FTTP to A&A in August (utilising my existing Openreach FTTP circuit) but despite the correct ONT serial number being provided by A&A's system when the migration order was placed, someone/thing managed to completely screw up the order so service was provisioned on a port on an ONT that didn't exist (records had been adjusted to indicate I had a multiport ONT when I still had and have the original Huawei single port one from when the service was installed in Jan 2018)

As I was without service and working from home I quickly had to get a working solution so bought a Zyxel NR5101 router and a Three prepaid (until December 2025) SIM.

Connection finally went live in September and did think about trying to claim some of the cost of the kit back from BT (by writing to their CEO) seeing as it was their balls up but an avalanche of work hit and that got put on the back burner and it's probably too late now.

I left the Zyxel in place and set the new connection as primary with the mobile as failover.

Unfortunately I've been affected multiple times by A&A's recent troubles with their LNS hardware, the mobile failover saving my bacon when it dropped during the working day, I know they are working hard on this and this is not a whinge.

Unfortunately rhe Zyxel hardware doesn't appear to support automatic fallback to a wired link so every time their end drops and recovers I have to go into the web UI and restart the connection.
I do want to retain a mobile backup but would like a solution that falls back without me having to do it and particularly as will be moving to digital voice.

Reading the documentation it appears it would indeed support this but interested if anyone has expeirence of this model or any of their routers in this or a VDSL configuration, thanks.