They didn't "soot" up. Changed glow plugs about 3 or four times. Other than that, the only issues have been one general cleaning on our current boat after about 12 years of use. We use it when sailing in Spring and late Fall in the Chesapeake -- and occasionally offshore and in Maine/New England. Over the winter, when I come down to mess around on the boat, I'll put it on.
I like Espars a lot.
Caution: Do not use a two level fan setting -- that tends to promote incomplete combustion; and, you need to make sure that you installation is done properly with respect to making sure that you don't induce to low a flow.
We ducted a return from the inside of the boat rather than pulling-in "cold" air.
I've only heard good things about a hydronic system -- but you have fan coil units, piping, and pumps to deal with. It has the advantage of almost "automatic" zoning in individual cabins.