Plagarized this from the web.
FUEL MANAGER - PRIMARY (PRE) FILTRATION
Primary filters, sometimes called a pre filter are plumbed before the factory filter.
passes through this relatively coarse filter first before continuing on to the vehicle’s factory installed filter, then to the high pressure pump. The filter media in a primary filter is rated at 30 micron. A micron is a unit on length equal to one millionth of a metre, or to break this down further; one micron is one thousandth of a millimetre.
So, a 30 micron filter will remove particles the size of 30 x 1,000ths of a millimetre. This may sound very small, and it is, but not small enough to protect modern high pressure fuel
systems from abrasive damage. Most factory filters on modern Common Rail systems are rated at 10 micron.
FUEL MANAGER - SECONDARY (FINAL) FILTRATION
Secondary filters, sometimes called a final filter are plumbed after the primary filter.
Fuel passes through the primary filter first before continuing on to the secondary filter, then to the high pressure pump.
The filter media in a final filter is rated at 2 micron or 5 micron, depending on the vehicle. So, a 2 micron final filter will remove particles the size of just 2 x 1,000th of a millimetre. Now that is very, very small!
So if the filters you have have the same micron rating, 2 of the filters are redundant. Best I could find was that the Ryco filter was 19 microns, so it would be good (though a little fine) for a primary filter. I couldn't find a rating for the Crosland filters, so who knows, maybe you're ok or maybe you've got the filtration reversed.
Kind of the industry standard is 30 micron primary and 2 or 5 micron secondary. Quality filters will clearly state what they are, and are usually available in different microns for the same filter head