Despite the cracky premise, the author manages to blend the two worlds without compromising too much of the characterization of the characters from either 'verse. The concept of Jashinism is explained in a way that 'balances' Hidan's bloodlust and Harry's boy savior qualities. Harry knows that Hidan kills people, but let's him keep doing it because he considers Hidan family, and as a result doesn't want him dead; Hidan has his own morals (he's particularly adamant about not killing children), and considers the AKATSUKI to be his family.
Nothing feels overly contrived, and even when it's a serious moment, there is still humor involved, though it is on occasion rather macabre. Overall a good story, and one of the more original plots available on the ever-bountiful FF-net.