The oem sensor was for my impreza at £306.
I cleaned the inlet on my impreza, and levorg, and my impreza was clean before I started.
My levorg was like a dirty diesel, and although it felt much more responsive after cleaning, it didnt improve mpg...
If Esso is better than momentum, I'll get that as it's the same price where I am.
Vpower however, is about 10p more.
I read an interesting thread on scoobynet.com about o2 / lamba sensors clog up with carbon build up and all they need was a blow lamp to make it red hot to burn the carbon away...