I don't think it's a fair comparison yet. We have no idea what to expect from Giddens. I like what I hear though. Apparently he rebounds well, plays hard, has long arms (like Posey), and can knock down open shots. And keep mind, not only is he a 4 year college player, he's also older than Pruitt, O'Bryant, Rondo, and Big Baby.
So he seems to have skills that will compliment the Big Three quite nicely and he seems to have plenty of experience. But time will tell how that translates to the NBA game.