Bit of an update in terms of Giganet...
I eventually went down the complaint process, and received an apology for their lack of clarity regarding the one-off charges. Apparently, in my location (postcode linked?) they utilise Zen as a supplier who in turn operate off the Openreach network. Zen charge them a service activation fee, which they must pass on to their customers. Also, they confirmed that these one-off charges are charged on placement of order and not on the go live date. However, due to their lack of clarity, they waived the fee for me
My go-live date of 3 Apr was unaffected. I received the Eero Pro 6E router via DPD a couple of days in advance (even though I'll never use it, as I have my UniFi kit in place). My exisiting FTTP disconnected at approx 00:30, and the Giganet FTTP was live as soon as I changed over the PPPoE credentials, which I didn't get round to doing until around 09:30. All in all, pretty seemless!
Since go-live, the service has been rock solid. I went for the 500down/70up @ £37/mth and speed tests have been constantly 490+/70+.
Their customer service is so s...l...o...w it's painful, however putting the complaint in did get a more timely response.
I'm still looking to get a static IP assigned, but have been told that they don't currently offer static IP addresses, though they hope to be able to offer these by the end of the month. I won't hold my breath!
TLDR - solid broadband service, awful customer service