I asked the same question a couple weeks back......took a wee while to get a answer but basically they are to expensive and don't really cure the problem......although I did read somewhere that someone had blind spot mirrors and were a huge improvement so I went down this route and they do help big time......and got a pair of Summit blind spot mirrors for £3.79 free postage (don't buy these from Halfords £7.99 each....ffs)