I am one who would like something more definitive than a deafening silence, but it doesn't have to be nasty.
Things like:
1. I had one of those and didn't feel the need to get another or even to fly it much.
2. Several of us at our field had one, and while they were OK, we had the following problems.
3. Not the greatest out of the box, but if you do this it can be a winner.
4. Not the best, but a great value for the money.
5. Looks aren't to my taste, but flies really well. (Or visa versa in some cases).
Or specifics about a bad habit or feature. Think of the Tango glow model, which some people can't get off of the ground due to its ground handling characteristics, but which gives no problems to others.
For someone who spends as much time at this as Bartman and Sleepy a silence speaks deafening volumes. Not so much for a beginner or someone who finds themselves being drawn be many things other than RC.