The AD60 is certainly an interesting engine to run and control. Like John said, the two unequal water tanks can be a bit of a challenge to balance, but with practice, the water levels can be anticipated over a given amount of run time. The boiler steams quite furiously and the engine has plenty of pulling power. I always thought of it as being two GS-4 frames under one long boiler, with smaller drivers. The design and layout of the systems make it a very forigving engine, but it can be a workout too.
They are far and few between in the US, in fact I know of less than half a dozen that actually have been out and run. I believe the majority of the production went overseas, but the production numbers are also very low to begin with. They are a rare sight indeed, always a treat to see one running and pulling long hauls like ti was designed to do.
Also, the re-release is stating that previous minor issues will be fixed. Not having owned one, I have no idea what they were, but I do think the engine will become more user friendly.