If you get to the Returns policy through my link, it says how to do it. (Despite what it says in the sales blurm about being returned new. I've never had to return anything to them.
Equally, how often do ordinary people post on forums about non-problematic returns to any reputable
company? It's just not something people do except in reply to someone who had a problem.
I have a vague memory of asking their CS back in an 2019 what would be the position if I bought the earlier version, and the reply was as long as the router was undamaged and the packaging OK, then no problem. Bin the SIM but have to pay for any data used. I guess that would have been at their 3-2-1 rate which would be expensive if you used much.
You'd need to ask them really, to get the answer to that.
Maybe a better idea would be this router from Amazon
with your current Three SIM? Easy enough to return to Amazon.
Though that still wouldn't solve the bridge mode question. It might handle a backup setup, (from the product description). Maybe not.
Perhaps best to forget my suggestions! (:
As for load balancing, I think you need to be talking something like Draytek stuff
. Or is your router similar?
My broadband basic info/help site - www.robertos.me.uk.
Domains, sites and mail hosting - Tsohost
Connections: OnePlus 8 Pro max 165Mbps down, 24Mbps up on Three, and B311 4G, tbb tests normally 35-45Mpbs down, 65Mbps off-peak, 9-24 up.
To argue with mindless bigots is foolish.