Actually you can do this for free and just leave the project on the thread and let the critics come and tell you what they honestly think about your project. But since it's part of your condition that you don't want to get anyone to talk about it to the public. I guess this is the type of project that you must be working hard very well and the idea that shouldn't come out before you launch it. The pay is good and I think you'll get more reviews with legitimate people if you post this on the
Services as said by Abubhakar. There are actually good reviewers there that will definitely give you the best impression that they've got for your website and everything on this project.