Yes, it combines water heating and space heating, so it is compact and the electric element (in the Plus versions) serves as an alternative heat source for both (dual propane/electric is common for water heaters, but generally not available for furnaces).
It has dual rates in the Eco version (three rates in the Comfort version), so it can run at a more moderate rate when the full output is not needed, which means less cycling on and off and more even heat.
I'm not sure if the water heating performance is great - I've seen comments from dissatisfied users, but don't have a specific link or quote. It doesn't have enough heating power to keep up with a high water flow rate indefinitely, and it has only 10 litres of water capacity.
I think that the separate fan motors for combustion air and air circulation would be desirable. In conventional furnaces, one motor drives both fans: as a result,
- cold room air is blown around during the combustion air purge cycle
- this is uncomfortable
- this transfers interior heat out through the unheated heat exchanger
- outside air is blown through the combustion chamber after the burner shuts off, until the heat exchanger temperature comes down enough
- this wastes heat, by blowing it outside
- running an extra fan on these ends of the cycle consumes extra electrical power.
The dual-motor design of the Truma Combi would eliminate this undesirable behaviour.