I've just had a quick play around with this and I'm not sure how much more helpful it is than other relationship predictors though I can see that their various graphs are showing an improvement. However, I tried it with one of my matches who is a documented half second cousin with whom I share 137 cM over 5 segments, and half 2C falls into the most likely group at 52.8%. However, my sister shares 322 cM over 11 segments with this cousin and half 2C falls into the lowest probability group at only 0.7%.
I then tried the sibling option where I could run the above search with the DNA details entered for both me and my sister. This time half 2C fell into the second most likely option at 20.6%.
I then tried an unknown match with whom I share 267/12 and my sister 206/9. On the search using both I came up with an 84.9% chance of the match being in the 2nd cousin group. For me alone it was the same group at 61.9% and for my sister the same group at 77.9%.
So where does that leave me? The 2nd cousin group includes 2C, 1C2R, Half-1C1R, Half-2G-Aunt/Uncle/Niece/Nephew, which is quite a range in itself, but from my experience with the known match, I can't necessarily rely on the most likely group being the right one. So I'm not really any more the wiser about my relationship with the unknown match than I was from the Ancestry predictions.
Anyway, that's my experience for what it's worth.
