Heres my 2p worth.
I run a lpg van for work. ive had it 20 months now in total and done over 25000 miles
So far ive had to buy a new fill nozzle ...thats it. nothing else has gone wrong. i have it serviced every other year.
Nothing has ever been replaced or repaired apart from the nozzle.
It does a little less mpg when on gas,the change over is unnoticeable and power loss is very minimal,virtually undetectable.
I run a bmw 330 ,wished id have got it done when i first bought it.
It runs a brc mulitpoint system often to be regarded as the best, ALWAYS get any work done by a reputable qualified fitter.NEVER diy imo.
Plenty of garages about. i have work done at central garage in doncaster,they are very good at what they do and are good on prices.