Openreach do charge ISPs a fair bit for fibre migrations, though I think it is less than an initial installation. There is no engineer visit.
You could look into TopCashBack and Quidco, or you could ring Plusnet and see what you can swing,
"on behalf of your parents who you can only just about persuade to move away from BT for the broadband and no chance for the line ..."
sort of thing. (With a cashback site as your falback option but don't tell them that).
You are correct about all you need to do is swap the router for the one Plusnet supply. (£4.99 postage).
I believe they get to keep the HH3. I don't know how easy it is to use it on other ISPs, but if at some stage you feel like setting it up on PN then you know you have a backup.
My broadband basic info/help site - www.robertos.me.uk
| Domains,website and mail hosting - Tsohost
Connection - Plusnet
Extra Fibre (FTTC). Sync ~ 53.5/15.2Mbps @ 600m. - BQM
"Where talent is a dwarf, self-esteem is a giant."
- Jean-Antoine Petit-Senn.
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