I was looking into the both the stillen and vortech yesterday. From my research i found that the stillen is the worse value in terms of raw bhp and that the vortech has seen some very nice output figures. As for the cost i'd imagine that the price you see in dollors will be quite comparable to it in pounds. As for the install i'd have a crack at it my self as i looked through the install guide and seems quite do able. You would need a remap and tune though