I have a 5 inch porc puffer in my reef for 2 years. Started out small.. about 2 inches. He is fat!! I do not have SPS. I only have softies. They are pigs!! My puffer is very active around feeding time... Only for the frozen shrimp I buy at the store for him. My wife feeds him ALOT. probably 5 peices of large coctail shrimp 2x a day. He is hand fed and has no problem eating from my hand. If I let him, Im sure he would eat till he died. lol. After he eats he goes over to a rock and lays on it and rocks back and forth from the powerheads and bothers nobody.. just happy to be full.
I have NEVER seen him near a coral. However my CUC seems to be dissapearing but I dont know if it is the hermit's eating the snails lol.
I will say, they eat A LOT, Thus Poo.. Might not be optimal for SPS.. Dunno, My nitrates are always around 5-10.