I own a Santro GLS( CNG) .A Hyundai fitted CNG version of the vehicle & the performance of the vehicle on CNG is very good.It is a value for money.It has a better ride position than the i10.i10 has got lesser head room as compared to santro.A must buy for people living in Delhi( NCR) as the running cost as well as the compactness of the vehicle gives you an edge over the others.Beware of the CNG kits being fitted by the hyundai dealers.Always ensure that your vehicle is fitted with CNG kits from the manufacturer i.e. by HYUNDAI.