On Sun, 5 Jul 2015 16:47:29 +0000 (UTC), Adrian wrote:

I've got (TP-Link) powerline here, not just across rings, but with one
end on a separate consumer unit daisychained off the main one.

No difference really.

Works just fine.

Define.

Is that browse the web over a 3 Mbps internet connection with no
noticable difference with or without the powerline segment in use.
Provided the powerline segment is faster than the internet connection
things will appear "just fine".

Or transfer a 1GB file locally with no noticable difference in time
taken if the powerline segment in used or not.

Aside from the RF interference aspect, it's more things to go wrong,
get zapped by lighting or mains glitch, lower speed, doesn't work
without power, than a nice bit of pretty much fit and forget Cat 5e
cable that'll be good for 1 Gbps, full duplex. Cables drawback is
speed of installtion and the requirement to know how to use a hammer.

--
Cheers
Dave.