They are quiet, but not so quiet I wonder if they are running. I can pack with carbon, bio beads or whatever I want for the results desired. Not a few inches of 4 or 5 items that individually are not enogh. I like the simplicity of construction and the ease of assembly and disassembly. The internal flow path is direct as can be, not weaving through chambers reducing flow. Minimal flow reduction, unlike other filters in service from what I have seen from friends who have other styles.
In 30+ years of using them, I have never, repeat never, had a failure of a motor, impellor or gasket leakage.