ok, i sell HSD but i also sell Sachs, Ohlins, BC and Tein, as well as ran 99% of them on my various evos. you will get people saying they are terrible and some folk saying there great. just my ten pennies worth is that for what they are i.e sub £1000 budget coilovers they are great, there are a handful of owners who have had some issues with knocking but you will get exactly the same with tein and BC, there are a hell of a lot being used so you will inevitably get a hanful that have defects
The next step up in the sub £2000 bracket you just wont get a great deal of poor feedback, they will do the same job but ride quality will be a hell of a lot better, for these you looking at Sachs @ £1500 or KW @ £1500
although teins are just over £1000 for most types, i would put them in the sub £1000 category in terms of build and ride quality
we have sold around 7 sets of HSD and never had anything but happy customers