Two things
1. Yes there is always exceptions to the rule and you will here about people keeping things that for all accounts should not work, but as long as you know the risk going into this and are ready an d prepared to risk certain things then your tank is your tank. IF you have success then share it with your experiance and it might help others.
2. Puffers have fused teeth that will continue to grow till they die, they use this teeth to break open clams snail crabs and what not. If they dont have things like this to help keep there teeth worn down they can and will chew on everything from rocks, corals, power head, your arm if its in there to long. If they dont their teeth will get to long and cause them to not be able to eat.
Now with that said the valentini puffer along with the stars and strips and a few others in the sharp-nose puffer family tend to be the more docile and less destructive of the puffers. If I was ever going ot try a puffer in one of my tanks it would probably be a A valentini, but I would not have any of my prized pieces in there with him at the time. One of the reason the above people are having success with there puffers are since they mention leathers and softies, which give off a nasty slime that the puffer may have tried once and said no thank you.