The board you linked isn't a galvanic isolator, it's just a capacitor bank covering a bunch of different frequency ranges.
The ADUM isolator I linked as well as flyback converters use transformers to provide a high-voltage isolation barrier between the source and device being supplied.
Transformers are generally larger, more expensive, and less efficient than non-isolated DC circuits.
The POE supply itself is isolated (with a transformer) and doesn't need to be noisy necessarily - but if you want even more quiet, another level of isolation can't hurt.
The ADUM isolator I linked as well as flyback converters use transformers to provide a high-voltage isolation barrier between the source and device being supplied.
Transformers are generally larger, more expensive, and less efficient than non-isolated DC circuits.
The POE supply itself is isolated (with a transformer) and doesn't need to be noisy necessarily - but if you want even more quiet, another level of isolation can't hurt.