Physically they are the same, same chipset, components etc. the main differences are what comes in the box (filters, cables, instructions) and the software. The software on the fibre router converts LAN port 4 be being a WAN port and disables the ADSL port. It's possible to install the ADSL software on the fibre router and vice versa but it can't do both at the same time. So we either have to send a new one out if you upgrade from Plusnet ADSL to fibre, upgrade it remotely ourselves or send you instructions out and how to switch it over.
Doing it yourself would take away the plug and play simplicity for most people, while upgrading it remotely requires impeccable timing (too early and you lose service for the morning of the appointment, too late and the engineer has already unplugged the ADSL).