I had a 2004 civic 1.6 Prosmatec. The CNG was such a success that people used to be jealous. no shifting problem, no idling problem and mileage was exceptional.
bottomline is it all depends on setting. My cng kit was not even efi!!!! that is the car always stayed on cng even on starting.
there is no problem of CNG on any car. it all depends on the setters settings his experience and your luck.
i will recommend you to go to mubarak cng in g-10 and first get the kit (gaspetro is also an argentinian alternative to landi renzo) installed WITHOUT lambda and see the results for a month. Get the best settings and keep an eye on mileage.
Ultimately when you think (of course through pakwheels) that your car is giving a good mileage, then you can think of lambda etc.
and I personally think there is no need of sequential injection kit right now.
whereever you go for installation please ask for a fine cylinder placement to get maximum trunk space. some installers do a very idiotic setting which deprives you of a lot of useful space.