In my opinion, Don't get CNG. 42k is alot of expense on CNG since gas prices are increasing continuously and are expected to rise further in the coming months.
If you drive around 5km/day and your petrol engine is properly tuned you should get somewhere around 13km/liter which means, you will require roughly 3.5 liters of petrol everyday. Thats around 338 rupees. On CNG the same 50 km will cost you around 200 Rupees of gas (roughly) . you will be saving around 135 rupees a day. if you drive 30 days a week you will save around 4000 Rupees/month. It will take you around a year just to break even with the cost of the kit. That's one full year of problems,frustration,quicker oil changes, tempering with car electronics,wiring, sub par performance,loss of boot space and engine wear. Not to forget the CNG load sheddings,long queues etc.
OGRA has continously been trying to bring CNG & Petrol at the same level which in current circumstances of low gas pressure etc seems totally possible. Enjoy petrol its the best thing!