I've got a few Devolo's around the house, they work fine between rings and on extension leads, though there's a bit of speed loss. They're the early 65Mbps (80Mbps? I forget) ones and I've had them for years.
One proviso when running between ring mains- because the signal has to go via the consumer unit it can be more prone to noise being generated on any other ring main. That includes the lighting circuit, and if I've got any CFLs switched on then I can forget about transferring data over the mains
It may be peculiar to my CFLs of course, though they're branded items not cheapo anonymous imports.
Edited by billford (Thu 27-Dec-12 08:50:50)