Feedback is absolutely essential to a forum. Problems arise when feedback is given with shades of condescendence. Point things out, but do so politely. I think Bob has been tactful.
However, something like this happened to me with my MTH NYC F7, after 3 years of its release a forum member kept repeatedly pointing out a mistake in the paint job that almost everyone knew about it and was already discussed. But the way it was stated was rather rude, as in between lines was saying that no matter what the set was worthless. Wanting nothing to do with that discussion, I made a comment about King Kong's sex life. While the comment was pretty dirty, I did not offend anyone. The comment was removed. Funny how language works.
This is issue is also tied to the fact of wether you own the piece in question. If you do own it, feel free to be as harsh on the model as you wish. Do so in first person. If you don't own it, measure your words and criticism. You may hurt someone's feelings. This hobby is expensive and making someone feel like they wasted their money is not cool.
I started with MTH engines myself about 4 years ago, little by little I am educating myself in the amazing universe of trains and modeling. Soon I'll get my first Atlas engines, and later in the future I'll look into Sunset and OMI a models. I know I'll never get a perfect engine, but like many people I have a soft spot for MTH. If it wasn't for them I wouldn't be in this hobby, and getting a purple box gets me so excited.
One last thought. I have seen people be aggressive towards new o scalers over accuracy issues. How does anyone want the 2 rail market to grow if all they do is push people away? Be welcoming and educate, without false modesty and the need to be the smartest guy in the room.