Underbody CNG tank on new Brezza, worth waiting for or fit a kit on mine now?

Saw on Team-BHP that the facelifted Brezza finally gets CNG with an underbody tank instead of the usual boot mounted kit. Mine's the older petrol, so boot kit is my only real option right now. For those running CNG on the current Brezza, how much boot space do you actually lose and is the mileage saving really worth it for daily office runs in traffic. Thinking of fitting one before fuel costs climb further, or should I just hold off and wait for an underbody tank setup to trickle down.