I just bought a boat that has CNG. I was concerned as availability isn't great for CNG.
Now that we've had the boat for 6 weeks, we've decided we like the CNG and don't plan to change it as it would be a pain in the butt to do so.
THere is a safety factor that propane doesn't have. If there is a leak, the gas rises as opposed to settling in the bilge as propane will.
Previous owner said he only had to fill his tank once a year and I can deal with that easily.