The parts for the Jxr are surely expensive than gti, but i kept baleno jxl same engine as jxr for over 3 years on cng. gave me no problems. i even put an after market intake, pipeline & exhaust.. its all about maintaining.. coils harddddly ever malfunction.. mostly if it starts to backfire, its either the valve clearance (tappet) or the wiring for coils.. (wiring costs 2.5k from bilal gunj). i had to replace my wirings once in 3 years.
This was about 1.3. but now yes, 1.6 is more hassle free on cng.
rest you have to decide which one you want to get.