CNG is cheap, but getting it in Rawalpindi and Islamabad is a problem. It opens for four days a week, but very long queues and one has to go very late in the night or very early to fill CNG which disturbs the daily life.
I have CNG in my 2005 corolla. I installed it after three years or running on petrol and since 2008 it is working MashaAllah without a single problem and giving me exceptionally good mileage Last week a full cylinder ran for 270 Kms, normally it gives me 230+. But the problem is filling time. This month I bought a Mehran Euro2 as a second car for local grocery shopping and I did not install CNG in it for the same reason.
A proper CNG set up would not harm your LIFE, but getting CNG is a problem, but you have a driver whom you can send for refilling. Key is original kit, emulator and advancer and expert fitter, then there is no problem.