I think this topic needs to be put in an archive somewhere instead of having a big debate about them all the time.
People say no
other people say yes
I got an improvement from mine when i had the astra but i havent bothered to get one for my current car.
make your own conclusions from that.
If your engine is badly out of tune, fitting an Ecotek might give an improvement in fuel consumption and smooth running. If your engine is well tuned and looked after, the Ecotek will just take away some of your good work.