I think Regner tried to make them a compound like the real one is with a high pressure and low pressure cylinder, which doesn't always work that well in live steam in this scale. I have the TSSD Mallet that is an abomination of an steamer right now. I am going to convert it to simple operation with some enhancements to the burner to keep up with the increased steam consumption and water usage. I will also have a Stainz again soon, I used to have one and other than needing to open the throttle really wide open to get it moving, it ran well. But with such small cylinders, it needed the throttle opened wide to get him moving and first, then quickly closed back down to prevent a runaway, much like the real locomotive. RC helps with this a bunch. I still hope someone else does the U class someday that runs better. I wonder how well the Regner Harz 2-10-2T runs? Here is my old all black Staniz running a few years ago, wish I still had it.