Vios 1.5E M/T Vs Mazda 2 1.5 Groove M/T

Hi all, need a little help here the wife is wanting a new motor before the first time buyer's scheme end's and her choice's are the vios and mazda 2 both m/t she plan's to drive about 10,000 km/s before switching the motor to lpg, so i ask if any forum member's have such car's and have allready made the lpg change and if so what about the warranty i guess the engine side is void and down to the lpg insurance to cover any miss giving's????? any-all advice welcome..............