Personally I think they are fine for short range fleet vehicles but I wouldn’t want one due to the shorter range between refills.
Way back in the olden days of the early 80s they converted our school buses to propane but they had switched back to gasoline by the 90s.
Range is a function of the tank. Tanks can be measured in gge (gallon of gas equivilent) and multiple tanks can be added to improve range ... the trade off is space. Larger vehicles such as trucks can make this trade of a lot easier than a mini-cooper.
I should disclose that I plan to convert my truck to NG as prices here in Colorado run between $0.85 to $1.35 / gge. On a 15 mpg truck, that can add up to a huge difference. ON a 40 mpg hybrid, not so much.