I bought this car from FX Hyundai, Faridabad in January and have been driving around 70 - 80 kms every day. I got the CNG kit fitted by Hyundai before delivery. They charge a whopping Rs. 60, 000 extra for the CNG kit(which is probably around Rs. 30, 000) in the market. The justification for this exhorbitant cost is that the warranty for the car will not lapse in this case(You will loose warranty if you get CNG kit fitted from outside). The performance of the car is satisfactory although it will take me a good 2 years or so to recover the cost of CNG(in terms of fuel savings) at the rate of 10-12, 000 kms a year. Three major draw-backs are:
1) Engine pick-up: You will curse CNG kit if you have four people sitting in the car and you are driving on a hilly road. The car just lacks the extra juice that it gets with petrol. This is a compromise with CNG which should not bother a fuel-cost conscious customer.
2) CNG filling: It is really a pain the neck to get CNG filled every alternate day. The cylinder size is 8 kg and with 70-80 kms driving every day, I get around 180-200 kms per full tank. Therefore, I feel miserable standing in the long CNG ques(which some times takes 30-45 mins even at 7.30 AM) every alternate day. Although I must say, more and more CNG stations are being opened in the NCR and it may get better eventually.
3) Boot space: Unlike in other cars such as Maruti Omni or Hyndai Accent, you do not get any boot space in this car.
Hope this is helpful.
GM