It's simply unfare that you judge a plugin by your inability to understand it's use.
You're not helping other users nor helping the developer, since you didn't bother to corroborate your statement.
If take the time to make a review, I would expect you to back-up what you say, giving examples of what went wrong and what you're trying to do with the plugin.
I've tested dozens of plugins just to learn what they do or how they're made, some of them I can't understand or make use of, but I won't bother the developer if it's my own inability in stake – unless I really want to use the plugin and have a serious question.
And I'm not just saying this because I don't like to give poor reviews. I gave my own bad reviews in the past. Maybe I was wrong, but at least I backed up my statements.