Cool sites - I like this idea of sharing concepts and getting feedbacks. One other larger one is producthunt.co. I'd be curious to see a full list if you happen to do some more competitive research!
This is why I don't like posting my product ideas publicly for anyone who searches keywords. If I give away all the details of my implementation, I could be helping someone else who is doing "competitor research." If I don't give the details, then my idea sounds incomplete or just like everyone else's idea in that space. No matter how many articles I read on HN that ideas are worthless, I still feel reluctant posting my best ideas on a site like that.
But I have a solution. It's called Indie Developer Club (see my profile for link). All the meetings are small with less than 10 people. You can show off a pre-release demo or talk about the specifics of your project, but you aren't posting it for the world to see. So you get some feedback but you don't have to worry about a competitor Googling you.