It's hard to say what may have an effect on their decision across the board. You'd have to know something about each one in advance to know what's most likely to influence them.
So my suggestion is to give them enough details for someone who doesn't know what you're talking about to understand what you mean.
What I mean is, if you believe a review of their site will be valuable to them, be sure that when they're done reading your email they believe it too.
The one caveat is that some programs may not want reviews done of their sites and you won't get anywhere pursuing those.