We are newbies and only just replaced our butane canister stove with a 800D with the blower lid on our Tomcat 255. Thus our experience is very limited, but quite positive so far.
We did spend a night on the boat and were quite comfortable, even though the temperature got down to -2 C and the docks were covered with thick frost in the morning. The berth area did run a few degrees cooler than the main cabin, although I suppose a small fan could be used if that was a problem. For us it was fine.
In those conditions we had it running pretty much continuously for a couple of days and it may have used as much as 0.1 l of diesel per hour. The fan does make noise, but it was a steady white noise and didn't bother me, even though I am a very light sleeper. As we wussed out and stayed at a marina for this test, we had shore power and so can't comment on the battery draw.
It does take a long time (10 minutes?) to start up and shutdown, so plan ahead for a cup of coffee and shut it down in advance of arriving home if it goes through your house battery switch as it has to have power for the shutdown.
We were concerned about the many reports of problems with the Wallas stoves, but convinced ourselves that these all seemed to be based on older models, with few reports of problems with the more recent ones. Time will tell.