Vortex XL Diatom Filter

Well a diatom filter is just like you said - a water polisher. That's pretty much the pros and cons.

It works to filter very fine particles from the water column, making it appear sparkling clear.

But it's not exactly a necessary item at all.
 
I hear that they work well for a minute and depending on your water they can clog up pretty fast. Just what I've hear though.
 
AquariaCentral.com