I use a sponge filter over my intake instead of the usual basket because I have sand substrate and need to keep it out of the impeller, and though it does require frequent maintenance it reduces the regular filter maintenance that I would normally do. However, I don't think any healthy puffer would have trouble keeping away from the filter intake. My
LFS where I got my freshwater puffers from has now started putting tubs of rock salt in the tanks with the same Malabar dwarf puffers that I have, even though they are strictly freshwater. Either they are trying to sell brackish puffers as freshwater and hope no-one notices the salt, or they are trying to sell freshwater puffers as brackish. I won't be going there again.... The moral is do your research and shop carefully.