As Andrew has indicated, once the FTTC Cabinet is functioning, it is very rarely opened.
Our FTTC is located about 10 Metres from our Lounge Window; and similar to your Friends, I can see inside it when opened.
It has now been working and upgrades available for 32 months.
Over that period, it has been opened about half a dozen times, once early on for the Stand-By Batteries to be checked and one possibly replaced, once for additional Filter Links to be added and recently a few times for more link cables to be added.
It is a Huawei 288, capable of providing 288 VDSL upgrades, to its associated much older PCP, with about 287 Phone Lines through it.
When the FTTC was first activated, only 48 Filter-Links were inserted, in the back-plane in the right-hand-side of the FTTC, and two, 100 pair link cables to the PCP.
The 48 Links restricted the possible, immediate working upgrades to 48 out of the 288 potential.
The two link cables restricted the future, easily done, to effectively 96 actual plus easy upgrades.
About 14 months later, 18 months back, another 48 Filter-Links were added, about a 10 minute job; and I was talking to the lad as he did it - he wanted to know the best way to another cabinet.
About 2 months back, another 4 100-pair cables were added, so potentially up to the full 288 potential of the FTTC.
The wiring of those cables to the back-plane took about two days.
I don't know if the Filter-Links to come up to the 288 total were added in that major exercise.
If they have been, then basically only the PCP needs to be opened for future upgrades.
As the average actual UK upgrade demand is about 30% per combination of FTTC and PCP, that explains why the relative long period involved.
At present, judging by the few visits to the PCP to carry out the final connections on an individual Order basis, I am doubtful if our FTTC has even reached the 96 intermediate capacity - and that is on estates where every house was pre-wired during build for phone services, reinforced by the speeds I observe on the TBB Broadband Map.