My car (in the display pic) was converted to CNG back in Aug 2009, when its meter showed 8000KMs. Since then, its going immaculate as it runs on cng. Petrol is not affordable as my travel is almost 70Kms daily. she runs 155KM with AC on a full tank of CNG - 8.5KG of gas.
no issues as such with pic, dropping RPMs etc. but yes, do get Landi Renzo's kit that comes in Suzuki cultus - the one which adjusts CNG to Air ratio its self, and controls idle rpm too. will cost you 10 to 15000 more than the generic after market kit, but your life will be easy!