My parents have had ADSL since before the "wires only" products came out. Back then, a BT technician actually replaced your master socket with a new type that had the microfilter built in.
The technician then ran a cable from the new master socket to an RJ-11 outlet near the PC (around 10m)
I just have a 10m RJ11-RJ11 cable plugged into my master-socket filter... works fine with my 1mbps broadband.
I suspect that the recommendation against extensions is largely to guard against people moaning they can't get it to connect reliably with a badly-assembled pound-shop lead, or through the extension socket they (badly) installed themselves.
The technician then ran a cable from the new master socket to an RJ-11 outlet near the PC (around 10m)
I just have a 10m RJ11-RJ11 cable plugged into my master-socket filter... works fine with my 1mbps broadband.
I suspect that the recommendation against extensions is largely to guard against people moaning they can't get it to connect reliably with a badly-assembled pound-shop lead, or through the extension socket they (badly) installed themselves.