I put it in once in a 2008 Hyundai i10 1100cc and in a 2002 Toyota Yaris 1000cc. Both had previously been running on the "factory" oils.
I’m not sure whether I saw an improvement in the Hyundai’s operation, but it definitely seems to be at least just as safe. I should also point out that Hyundai’s "factory" oil was a 10w40 synthetic-base oil. So the clear gain is that I have at least a 5% reduction in fuel consumption. The fact that it pulls a liiiittle better uphill may just be my imagination. I should mention that I put the oil in the Hyundai with a bit of boldness. I say this because, yes, the manufacturer recommends anything from 5w30 up to 15w50, but the Greek dealership recommends 10w40. I took the risk of doing the test last year at the beginning of June, checking the level throughout the summer every 100 kilometers or so, and although I’ve driven about 6000 kilometers since then, it’s questionable whether it has "drunk" 50 ml.
For the Toyota I don’t have much to say. The Mannol 5w30 replaced Toyota’s also 5w30 and I haven’t noticed any difference. In 7000 kilometers it "sipped" about 200 ml, but I didn’t even bother to top it up.
In a little while I’ll change their oil again and, God willing, I’ll come back after about a year.