The arithmetic then works out to 5.6 L/100km for the users in the first 100 km of the 300 km total. 42 mpg(US).
No, you misread. There were two trip meters. One had not been reset for 3000km. The second had a few hundred km's on it since we received the car.
I read: Meter #1: 300 km, 4.4 L/100km (combined use from you and before you) Meter #2: 200 km, 3.8 L/100km (your use)
You are missing a zero on the end. Meter #1 had THREE THOUSAND kilometers plus our usage on it. The 4.4l/100km figure I noticed early on. The 3.8l.km was our figure when we turned the car in on the other meter.
So your position is the Toyota Prius is the "only" better car, even though this thread is about non-hybrids. If someone buys anything else, they are an idiot. If someone else owns a Prius, yours is better. Got it!