That spec is pretty good, especially when combined with rogue so that shredding is more your option.
However I've found out that imp mangle talent is quite worthy, since it helps you stack the infected wounds fast, also combos, and mangle doesnt seem to lose much dmg per energy from shred if improved.
To me, Rend and Tear is very good talent, but yet has to prove that it needs 5/5.
My spec