Has anyone used these up stream O2's? With the recent thread started by Shaun@AED about either replacing the O2's every ~6 months or having the rear O2's active to allow the factory pcm the calibrate the fronts, it just got me thinking. My rear O2's are active but I've still replaced the upstream O2's 3 times in the last 4-5 months, all with OEM Ford sensors at $125 a pop. Luckily, this last go around I got one of them replaced under the 12 month/12,000 mile parts warranty. So I'm curious if any one has used them, looking for experienced reviews as they average about $50 retail. I would figure they are great as I'm sure Bosch most likely manufacturers them for Ford anyways, but still, curious.