That video looks like a backyard installation to me.

Here is a sample of an engineered solution. The WING system is not available for retrofit, or for your X5, but it gives you a basis for comparison, and the web site has good info on CNG economics.

Any kit that is using a mixer carburetor is not in the same class.

Westport WiNG

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2007 X3 3.0si, 6 MT, Premium, White

Retired:
2008 535i, 6 MT, M Sport, Premium, Space Grey
2003 X5 3.0 Steptronic, Premium, Titanium Silver
2002 325xi 5 MT, Steel Grey
2004 Z4 3.0 Premium, Sport, SMG, Maldives Blue