Just ran a few tests, my conclusion - it's useless (just like all the other valuation sites).
First test I ran, it gave a value of $144 for a site that brings in about that much on a good day. So it's out by quite a lot.
The other tests I ran were just as ridiculous.
There is so substitute for experience and sound judgement. Website valuation relies on facts that these tools don't have, and expertise that these automated tools can't emulate.