Last year's stats very similar to Brandon Joseph's:
Joseph had 30 tackles, 15 solo, one INT and one forced fumble.
Harper had 30 tacklets, 17 solo, one INT and 1 1/2 tackles behind the line.
For the Irish defense, Harper can be used all over the secondary, both at nickel and safety. But Joseph had much much better stats the year before he came to ND. I do think Harper adds some flexibility in the defensive backfield.