Hi All. The quality of fitment is as important as the kit itself.An experienced and efficient mechanic can do a better job than most authorized service centers. I had my 2011 Chevy Beat fitted with Lovato CNG kit (closed loop) around 7-8 months back, and have clocked 31000 Kms til date (20+ on CNG). It costed me around 28K including RC registration. Initially there was power lag during pick up and acceleration,but that is expected. When I got it tuned from my mechanic, this problem was also solved to a great extent.
Just remember to take care of your engine. I do my weekdays driving on CNG, and weekends on petrol. Running you car, any car, on CNG all the time will eventually take the toll on the engine.
Happy Driving!