Also why is an engineer visit required for a self install?
You don't want a self-install in case you have poor wiring at home. Having an engineer visit means you will get the best speeds possible from your home and the wiring in the street to the cabinet.
this is not always the case , i had an engineer install and he didn't do any checks at all , plugged the modem in after i told him which cable to use plugged the router in ,said all the lights are lit your ready to go. I had to check i was connected to the internet and did a speed test to find out what i was getting, He was a Kelly contractor even told me that they had stopped making the HG612 modem and that's why i had to have an eci one, left great feedback for him when they texted for it