If it's me you're referring, mine were bought from the factory as a propane units. The comparison mower was a EFI mower exactly the same as the propane unit from horsepower down to the blades and mulch kit. The only way to compare was to make the comparison units exactly the same aside from fuel source.
There is nothing wrong with the mowers running propane. There is a big problem, here at least, with actually buying propane in bulk. This is natural gas country and you have to go about an hour north of my shop to get into bulk propane country.
It is purely a supply issue for me, without my fueling station I would have not continued. I paid too much for delivery and tank swaps, the drivers were not consistent with delivery times and often filled my dock with bottles I had to move to get other deliveries, and worse, missed days on end. Until those issues are solved, propane is going to be a niche market.
No propane company I spoke with was interested beyond selling me an overpriced tank. National Grid paid the bulk of my CNG infrastructure (85%,) and the state and DOE paid the bulk of my LPG infrastructure (75%.) I would have thought propane was the Gillette razor model, give them the handle and sell them a lifetime of blades.
The numbers work on the machines, but there is more behind just the machine that is needed to make this entire system work.