First Timer here need some input

hello there! please bear in mind this is not a reef tank. set up my 75 gallon aquarium 2 days ago. did my research and went about setting it up according to many of the threads I have read. purchased the RO/DI water directly from the specialty store I purchased my tank and supplies from. put in 40 lbs of live sand that the specialty store recommended. I asked if I needed more and they said no, also their tanks don't have a ton of sand either. this place has been in business for over 30 years, went there a few times as a kid so I trusted their judgement and all the tanks look exceedingly healthy. I have the glass canopy top and fluorescent light suspended over the tank. the tank is CRYSTAL CLEAR and cycling nicely. here is the big question. why am I reading all these threads saying Canister Filters are a huge mistake? the place I purchased my tank from sold me an EHEIM 600 that is made for 160 gallon tanks. I told the guy that I read horrible things people said about canister filters and he said for reef tanks they aren't the greatest choice. he said in the future i may want to add a protein skimmer. my tank will be stocked with maybe 8 fish. clowns, a tang, some watchman gobys and maybe a puffer. can anyone shed some light on why canisters get such a bad rap if I use it in a lightly stocked tank?