I tried it too, and guess what, I too got presented with Henry David Thoreau! Tree correct back to John Hitchcock (1700, Oxfordshire), then it goes, Elizabeth Jones - Elizabeth Graves - Mary Church - Richard Church (1608 - 1668)
Parents of John Jones I have as John & Elizabeth (no marriage), and now find a hint for an Elizabeth Jones on Elizabeth's profile - born in Herefordshire. The only Mary Church that fitted the dates and married surname, was born, married and died in the US.
On top of that, for another of my great grandparents, it gave her the wrong mother. And never picked up at all on my grandfather's relationship with Thomas Hepburn who started the Miner's Union. Not that you'd expect it to, it's clearly fixated on the States, as usual.
So appears to be absolutely useless, at least for the UK.