Yeah, puffers are an interesting group. I have had multiple members of the same species with totally opposite personalities. One of the species would be highly aggressive while the other wouldn't even think about hurting a guppy if it had the opportunity. This may simply be the personality difference between sexes
but I am not 100% sure. My only advice is that each puffer is unique. You will have to use your best judgment. And even then, you may wake up one morning and find that the puffer is bloated from the midnight massacre of his tankmates! Use caution!