[CNGBiFuel]

I'd agree. The factory system is OK, but not brilliant. If you can find one it's the better choice because even if it's not working, the conversion (and the tank is where the work is) is broadly done, and done well. Find a good one, and it'll do what it's supposed to do. Burn gas.

You won't pay much more for the factory offering over without. Same applies to a conversion. The problem with non-factory conversions is the variable conversion-quality - sooner or later this leaves you still doing the job.
But now, you've the bulk of the parts to put it right.

Be aware the far rarer factory CNG (rather than LPG) have tanks in, (or very near) expiry. This worries most, not me - thus if you find a RHD CNG car, send it my way, and I'll sort it. Be careful, even dealers don't know a CNG car. I've got mine from people that bought them thinking they were LPG.