Purina One is not a good food for ANY breed, particularly a giant breed. Its low quality and has a ton of fillers.
I have my dogs on Innova Evo. Evo is the no-grain, all protien variety. Its too high in protien for giant breed puppies, but as he gets older its a great choice. I know a lot of people on this board feed their giant breed puppies Innova Adult.
The Evo has been great with my dogs, though. Cabeza literally eats about a cup and a half a day. (He's 100 pounds and a little on the tubby side) Their poop is almost non-existent, they have BEAUTIFUL SHINY coats, good breath, no skin itchies, etc.
When I first adopted Cabeza, he was on Purina one. He CONSTANTLY chewed his feet, itched his rear and his coat was dull and his skin was flaky. I highly recommend that you don't feed that product!