In what way exactly won’t a R6800 do justice to his connection? It’s capable of sustaining a WAN>LAN of more than FTTH can provide at present and is vastly superior to Technicolours offerings in both features and support, it’s a decent (relative to its peers) AIO consumer router. Personally i’d probably suggest considering the R7000 for DDWRT support if you want an AIO, but it’s not within budget.
I agree Unifi CPE is generally nicer to work with and superior to consumer grade AIO products, but the idea that he needs to spend that kind of money to do justice to his connection seems slightly out of place.