tgreggI believe the complaints you read referred to the earlier version of the Wallas unit designed for marine use and not RV use.
I've had 2 of the diesel cooktops in the past 16 years. The first one was this early unit. The second one was made after Wallas joined forces with Webasto and the unit was redesigned for the RV market.
In the early version there was no altitude compensation because it was intended to operate at sea level and it would run rich at higher elevations. In the 3 years I owned it I had it serviced twice for cleaning. The weakest point was the blower which was underpowered and caused the cooktop to be slow to warm up and cool down. I had to have the fan replaced once.
The newer redesigned (by Webasto probably) unit that I've used for 13 years has altitude compensation and has never required service. The blower for combustion air is more rugged and powerful and the warmup and cool down is much faster. Making a quart of coffee in a stovetop percolator takes less than 5 minutes to perk and then a few minutes more depending on how strong you like your coffee.
The big difference compared to a propane cooktop is that the Wallas / Webasto unit draws combustion air from outside the van so there's no worry of depleting the Oxygen if you use the heater lid and it exhausts the combustion gases outside the van as well so there is no carbon monoxide released inside and no moisture to condense inside the van.
Hope you don't mind if I try to update some of that 'old' information that still persists.
Thank you for your post, I really appreciate you taking the time to detail your experiences. I know you have lots of experience with this & I agree with everything you stated. Further is seems like they have fixed the finickiness of the diesel burning units. If I had a diesel PM I probably would have taken the chance, but my PM is gas. I only purchased the Wallas duo to use as a heater.
FYI; The Wallas Duo; after I purchased it and was reading the instructions; Detailed that the unit could take 11 minutes to start up. That was a start to me deciding to return the unit to the store. I like info like that upfront (my bad for not downloading a manual prior to buying). There were other "finicky" items detailed in the manual & I thought to myself this just isn't for me. I am sure it is a fine product - just not for me
To understand my choice of going to Propane, I will explain our use of the Van;
1) We cook with Propane so we carry it regardless
2) We only cook outside - Not in the Van
3) The only onboard propane appliance we have is a Propex heater - Oxygen Intake and exhaust combustion gasses are thru the floor of the van and to the atmosphere (no fear of the Oxygen /carbon monoxide from this system or from cooking inside)
4) If for some reason we wanted to cook inside, then we would use out "induction 300W to 1800W electric cook top" This will probably be unlikely, but there if we wanted it