While there is a recent thread on Ceratec here, thought it was worthwhile adding to it.
Recently treated my BMW 520d and my Wifes Dacia Logan MCV 1.5DCi.
I noticed no improvement at all in the BMW, nada, zilch. However, the engine in the BMW is very smooth and very insulated. Add into that the ultra-smooth ZF 8HP it's no suprise I noticed nothing at all.
I was dissapointed that I didn't notice anything treating the BMW and therefore was expecting the same when I treated the Dacia. Suprisingly there was a noticeable improvement. The engine isn't any quieter, I didn't expect anything different as the engine noise is mainly combustion. However, there is a singificant reduction in general noise and vibrations, ecspecially at lower RPMs. In addition, the engine seems happier at lower RPMs. The car is a manual, therefore it's easy to lug around all day. Before the treatment anything under 1500rpm was an unbareable, shudder filled turbo lag pit of doom. Now, it's smooth and happy right down to ~1200rpm before the drone of engine labour starts resonating through the cabin.
I wouldn't say there's any extra power, and I've not noticed any changes in fuel economy. However, I find fuel economy comparison almost impossible because the consumption varies massivley from one week to the next, anything from 35mpg to 65mpg depending where my Wife has been or what mood she's been in.
In summary, the treatment has made the Dacia a little nicer to drive and the engine feel quite a bit more flexible.
All in all, impressed and I think I will carry on the treatments. The Defender will be due a service soon and planning on running the Liquimoly flush, seal conditioner treatment and MS02 additive.