I recently picked up a secondhand P class for a reasonable price from a reputable dealer. Unfortunately when I tested the model it ran quite badly with a definite sticking point. At this point I probably should have packed it away and returned it to the dealer. However I knew I had no chance of getting a replacement, being both 2nd hand and the only one in the shop. I could have requested a refund but I chose to investigate further. Initially I thought the crank pins were catching the steps as they seemed to be very close. I tried to tighten the crank pins inwards to give further clearance but this did not improve the running. I eventually decided the issue was the wheel quartering as the coupling rods did seem tight in places. I persevered with this idea until I eventually succeeded. Now the loco runs exceptionally well. The pickups on the center wheel do look a little soft and not always in contact with the wheel, but while it is running so well I am reluctant to mess with it.
In my opinion the model, although not without floors, is an exceptionally fine example of modern RTR steam loco's and the main manufacturers would do well in using this as a benchmark. However, as with many RTR steam loco's quality control can be a little wayward (not sure how you'd get around this for the money).