I work for a company that tests air and water filters, so I know EVERYTHING you could ever want to know about filters... This is a very nice filter. The smaller the micron rating, the better the filter is at catching crap (efficiency). One think to keep in mind, the better a filter's efficiency, the quicker it will plug up. But seeing as you wont be running thousands of gallons through the thing, I would for sure opt for the 0.45micron filter. I know for a fact that Ebay has TONS of water filters and housings listed... you will likely pay much less going that rout.