Anyway, I've been playing with it, but I don't honestly think it's very good.
After some very poor results with photos of various members of my family (e.g. my great-grandmother had a higher match with one of her husbands, born in a different country from her, than with her brother), I eventually tried comparing myself with my son (the only person in my tree whose parentage I can be 100% sure about
).
The photo of him I uploaded had a poster of the Blues Brothers just behind and above him, which the software treated as another photo.
I had a 22% match with the Blues Brothers and only 16% with my son...