I got my CNG installed in ma City 2008 just 2 months back from CNG Complex Sarya Chowk (Mr. Sultan Akbar)... its the corner one right off the chowk. Till now the performance is OK and no problem alhamdollilah. The consumption got better with running after a month too, so i guess you guys can give them a shot.
Although I should warn you to stay on their heads till they finish the job and keep a vigilant eye, cus otherwise the mechanics just get distracted with the shear amount of cars getting CNGed that they sometimes lose track of time and car/kit parts. I mean just keep an eye on the parts that are dissambled frm your car or that comes out of the Dabba of your new CNG kit. I think this is a general suggestion as incidents such as described by earlier posters (Venturi missing, back seats not bolted properly after CNG work etc. etc.) are v common everywhere.