Petrol : 8.5km/litre.
CNG : 12-15km/kg
Duration of car driven:
Learn to drive like an uncle and you'll get used to the performance. Of course you can counter this by revving hard all the time to start off but that'll increase the fuel consumption. I always drive off within 2000 rpm & I'll pump the accelerator.
Performance aside, I feel really safe inside this car (safer than my previous 5-star safety car). The CNG option helps knowing that I'm only paying 2/5 on fuel now since using gas 99% of the time.