I can vouch for and against CNG cars as I've driven them
Managed 182Km on 8Kg CNG once- Santro 150,000km driven rental car.
So, if I can remember correctly, CNG was priced at 75rupees/kg last year? That means 600 Rupees for a full tank.
Now, this particular Santro does 12-15 km/l on petrol. Price last year was 92-100Rupees per Liter.
CNG was worth it for me, Rented car, CNG opened 3 days a week, any issue with the car, owners responsibility ( Good friend of mine).
Todays date- Not worth it. Long lines, CNG is kinda more expensive than what it used to be before.
I prefer Petrol or LPG. I just don't want to ruin my cars warranty by installing LPG.
TL;DR- Got a lot of time on your hands, CNG suits you. You can do Zikr/Tasbeeh/Homework/finish off work projects on your laptop while waiting for CNG- Rewards at the same time and no time is wasted.
If you're busy like me, Time is money. That's why I use petrol
CNG does save, as long as you have a fully maintained car and the car is in good nick, as well as the CNG settings.