When I was with plusnet, it was a thing to have to hop gateways to avoid congestion, but as I understand since plusnet moved to dedicated WBMC the issue of congested MSIL's is gone, but I dont know if there is any congestion on their dedicated WBMC. Need existing plusnet customers to tell you that.
Also I think is no working IPv6 on plusnet.
Otherwise the only other concern is their billing platform.
I might still be stuck with that problem as I read something about static IP customers being allocated differently on the network.
I went for Zen because being a smaller ISP, they aren't forced to apply blocklists like the main ISPs BT, Plusnet, Talk Talk, Virgin, etc. From past experience, ISPs with blocklists will on occasion cock up and block an entire domain just because one specific page appeared on a blocklist.
There's probably little risk of that happening these days, but on principle I don't like the idea of an ISP only giving me access to "some" of the Internet. Once I go FTTP, I will drop the Plusnet line and go Zen exclusively.