Okay, time for me to chime in on this discussion.
I have had extensive experience with CNG transit buses. I drove them for 4 years. I fueled them for 2 years, talked to the mechanics who worked on them etc. Here is what I experienced:
CNG is less efficient than diesel. Cummins and formerly John Deere have had CNG specific engines for a decade now. At first, they were converting diesel engine models to run on CNG, but now Cummins has the experience engineering etc to build them on their own merit and not copy a diesel engine.
CNG fueling in large quantities requires HUGE HUGE compressors. Fueling to 3,000 PSI on these buses would take much longer than filling a bus up with diesel that drove the same distance. Also, CNG compressors tend to fail a lot more than a diesel pump. CNG compressors require lots of electricity to operate.
CNG engines do blow up and require overhauls. Their turbos go out. They can overheat because they run hotter than diesel engines.
CNG works well for things like UPS and buses which have a planned route and home base where a large compressor house can be stored. For the public, there is still lots of work that needs to be done. Commercial over-the-road trucking LOL! Not going to happen for a loooooooong time.