Too many things to go wrong and if used incorrectly you need a specialist and they are expensive to fix. Plus they use fresh water
In my case probably too much paper and not enough water
followed by a second flush before vacuum was restored fully (by my son) resulted in a blockage somewhere. Impossible to fix myself and hard to find a specialist. $2,000 later on during our Xmas break it failed again. The boat
has 2 completely independent vacuflushes so I had peace of mind until the second one started not turning off when up to correct vacuum. Nursed it home by manually managing the vacuum switch so we didn't have to cut the break short but lot's of shore visits.
So better to have a simple system that can be fixed easily if you are remote
or everyone is on holidays. Not to mention the fresh
water usage and the cost repairs