well a month or so in and it's been a flawless experience.
the virgin install went live on the day they said it would, it required no home visit and the router was delivered on the day they said it would (some days well in advance of the install). i connected the router and and tested everything was working (as it was).
i then set the virgin router into modem mode and connected it up to my existing network config (edgerouter/unifi AP), and with a couple of tweaks of the edge config (changing from pppoe to dhcp) everything works as it should.
i'm on the vivid 200 package but any time i test my speed is averaging at around 215Mbps down (~26MB/s down). upstream averages at 12.4Mbps
is it possible that a plusnet migration would have been just as flawless? quite possible. did i have any faith that it would have been? not so much.
in the end i've got a much faster downstream for the around the same price as what i would have paid plusnet. upstream has dropped by about 6-7Mbps, but that can be managed.