On the subject of Swindlesaves, I came across them when they first hit the market, and thought, like you did, that they were exaggerating, and consulted the two leading experts who write most of the text books - Hugh Piggott and Paul Gipe, and found that they were excoriating in their comments - in short, roof-mounted chocolate teapots were a heartless con that would have required the rewriting of several laws of physics to have fulfilled their ludicrous claims (30% of your electrical needs in an urban area) - subsequent tests and real-life experiences bore out the experts views (many turbines generated less electricity than was needed to run the inverter)
Being the public-spirited citizen that I am, I did my best to warn people, and even wrote at length to B&Q suggesting that to market them was sheer folly........
Since then Swindlesave have gone defunct, and it cost B&Q a fortune in refunds............
Just in case anyone thinks I'm "anti-wind", I'm actually very much in favour, but they do NOT work in towns, unless you can get them up a 100' mast out of the turbulence, and mounting them on, or anywhere near a building, turbulence kills the performance stone dead.........and as a nice adjunct, building transmitted bearing noise has to be heard to be believed - one disgruntled owner complained that in a wind, his stair rods rattled!