As long as you compare apples to apples...
When it comes to filter ratings you will see pore size rating a lot of times...
This alone is not enough information to make any kind of educated judgement on filter quality.
It can be a nominal rating or an absolute rating.... a prefilter with an absolute rating of 1um means that no pore size is bigger than one micron. Whereas a filter with a nominal rating of the same size refers to the filter's "average" pore diameter.
In addition is the porosity rating of the filter... You can have two filters with 1um absolute rating, yet filter "A" may have 10x the number of pores of filter "B". This means that filter "A" will last much longer.
Both of these variables add cost to the manufacturing process....
Beta ratings are a better metric when comparing filters, but I dont know of any RO prefilter vendor giving Beta ratings. Beta rating is a comparison of the the number of particles of a certain micron rating coming out of the filter as opposed to the number going into it.
Spectrapure does rate their filters in "near absolute" values and total expected life expectancy in gallons (carbon block filters). They also offer membranes that are individually pretested with certified capture and rejection ratios.
This is not an endorsement of Spectrapure and you bring up a good point.... There are cheaper sources out there but this is sale on what is considered top shelf components
