What range would that setup give you on CNG?
I've had this system for LPG so it probably behaves the same.
Don't underestimate the complexity of this system and the tuning involved.
The venturi system is the cheapest but needs to be finely tuned and requires single pronged sparkplugs at 0.7mm gap to function at least decently. Then there's the fact that you just cannot floor it from standstill when taking off. Once you drive on gas this way you have to be a little more careful or you'll end up blowing **** up in your engine bay.
That said, your engine should not be bothered much with this and it acually runs a little cleaner.
Oh and don't put the venturi directly in front of the throttle butterfly or you'll have trouble with your idle. Right behind the AFM is easiest.
Expect to lose a little power too, because the venturi restricts airflow a little.
2008 audi A3 1.9tdi
(former 1991 520i LPG)