They do say "You get what you pay for". Just learned this the hard way.
Couple of years ago, the speedo died on my Focus, so replaced the speed sensor with one of those cheap OEM ones you get off Ebay.
Worked fine for about a year then it died.
Replaced it with another el-cheapo replacement sensor. Same thing, lasted just over a year then died.
Have now replaced it with a GENUINE Ford sensor, which I guess I should have done in the first place.
These cheap ones go for about £15 on Ebay. Genuine ones go for about £50. However, by getting the cheap copy, rather than saving myself £35 I've actually spent an additional £30 by having to replace it 3 times, when if I'd just bought the genuine article in the first place I (hopefully) would only have to have done this the once.
See how long this genuine part lasts, but it's got to be longer than those cheap ones.
Just a cautionary tale I thought I'd share.