Question On Converting Car To LPG

I am considering converting my car to LPG, but am uncertain of a few bits and pieces which I hope somone can help me with.

It will cost me £2000 to have the car converted, for which I can get a refund of over £1000 from the government. Fuel costs will be about 50% less, but PLG MPG is a bit worse than petrol. Doing 15,000 piles per year, I will save about £450 on my petrol bill. BUT: are there any hidden costs, such as annual servicing, insurance etc which will significantly whittle this profit away?

I would be converting a pertol Zafira to dual fuel. Apparently I would have to use petrol for starting the car. Can anyone confirm this? Is this the only time when I have to use petrol?

That’ll do for the moment, I hope to hear from LPG users.