youll have to read the small print for that company as theres a few around offering the same king of thing...
the trick is to have your dish washer/washing machine/etc set up on a timer to run while its nice and sunny outside
if you sell the house, they stay with the house, and iirc after 25 years they can come and take everything back.... but itll all be dirt cheap by then anyway
as long as you read the small print, and they replace any parts that break etc... then you have nothing to loose.
(most panels are guaranteed for 25 or 30 years anyway, but an inverter is ~£5k, most are only guaranteed for 3 years, and are expected to last about 10)
not much good for the summer, but for the winter you can setup a system so heaters can be automatically tuned on/off up/down to match the amount of power being exported so it warms your house up a bit :-)
if you want to spend a bit more, you could have it divert power to your hot water tank (if you have one) and heat that up instead
look here
http://www.navitron.org.uk/forum/(Im knighty on there too)
theres a load of people on there running these systems, or bought there own panels etc. etc.