I have had my King Tiger and Pershing now for some time, maybe almost 2 years. I use them on anything except pea gravel. They get stuck in the wheels and tracks and tear sh*t up. I have used them on dirt, standing mud, dead grass, tall grass, snow 'I live in Buffalo NY,' ice, carpet, 20 degree whether, NOT RECOMMENDED, 95 degree whether etc. I have used them in just about any terrain. the King runs better on some stuff than the Pershing. Larger foot print I am assuming. Every thing on my tanks are stock, no upgrades and they run great still. I am very careful not to run into stuff or go into puddles but I also clean them often. Preventive maintenance is key! I also try to avoid pavement as much as possible. I am getting close to puchasing replacement tracks for the King Tiger because of wear and tear. I have purchased spare gearboxes just in case I need to replace the originals, but alas the originals still are in great shape. The best place I have used my tanks was in a construction site. Nice hills, ditches, flats and tire grooves.
All in all, I am very happy with Tamiya's products. If I had to give a con, I would have to complain about the Pershing's stock idler wheel, not much adjustmenst can be made. The cons for the King Tiger would be the stupid pins for the tracks keep backing out and the aluminum barrel is either to heavy or the gun elevation unit is not stong enough to move the gun smoothy. I do not have a fix for the Pershing idler wheel unless I buy the upgrade. As for the pins backing out on the King, I use 'Lock tight' on the pins. The gun elevation unit, I have done some tinkering, some hard to explain, but it seems to have work or at least made the main gun move more smoothly.