This is interesting, but you will probably get better reviews and feedback through your network. It is probably better than sending generic cold emails to YC founders though (which happens and I would discourage).

While I am open to giving back to the community, this should really have a little more information on who's behind it, what a sample review looks like, etc. Also if the reviews are truly double-blind, it seems to take a lot out of the value for the founder. One of the big reasons I help many startups I don't already know is simply to expand my network.