So yes, I did have a photo of the label, thank goodness. Things seem to be much better now after the factory reset, the WWAN is showing as Failover: Enabled and traffic seems to be going in the right place.
The WiFi seems slow though - I did find when using the RTU950 WiFi in AP mode it was slow, and now in client mode it is delivering around 4-5 Mbits/s even with a solid WiFi connection (104/65 Mbits reported by the AP) to the same network as my desktop, which is showing around 80 Mbits/s on a speedtest. I realise it won't be as fast with another WiFi link in the picture, but a greater than 10x speed difference seems a lot.
Another question - I have added multiple SSIDs for the WiFi client mode, and it seems each one appears in the interfaces and failover list as a separate interface, requiring individual enabling and ordering. Is this as intended?