Although I'm a low-quality scripter, I agree with Xalos.
First of all, there's a difference between pointing out issues/flaws with the add-on, and using this issue to make the creator upset or just not caring at all.
Pointing out any issues or flaws is one thing, and it's extremely helpful to the creator. However, like your example, calling the creator a 'crappy add-on maker' or something else is just plain rude.
Second, if you're going to point out any problems, you should really remember that the creator probably worked hard (especially if the creator is still learning) on it and doesn't want some idiot coming in and bashing the add-on.
The same should go for server hosts too. I host frequently and I really don't like it when another host comes in and calls my server 'bad' or 'low-quality' without really giving a reason why.