Been running my GS for about 2 years now, Romano SVI (multipoint injection) system fitted with a 75 litre Stako toroidal tank in the spare wheel well.
Very happy with it, it's more than paid for itself.
Quibbles:-
At high load & high RPM (hard acceleration in PWR mode, for example) it can't get fuel through quickly enough and will trip back to petrol until you ease off the throttle. Bigger injectors would probably cure this, but apparently I've got "C" injectors fitted already, and bigger ones aren't available!
Power is down a bit on LPG (noticeable when you switch to petrol and the car suddenly has more oomph), could increase the fuelling to counter this (got the cable and the software to communicate with the Romano ECU) but this means it trips back to petrol (see above) at a lower loading.