Loren,
I have worked on a number of boats that had dual switchable filters and they do work but they are very pricey if you buy them pre-made. Personally I prefer a dedicated polishing system,
like this one I installed (LINK), which keeps the tank clean so the primary filters don't plug to begin with. Switchable filters are a band-aid approach from an injury you should have never let happen. Switchable filters don't solve fuel problems, they only give you a new clean filter with the flip of a valve so you can then plug it up too.
Racor wants to see pumps plumbed on the suction side for the most efficient water removal and also to facilitate the use of a vacuum gauge. The problem with vacuum gauges is that in many installations I see the owners have no idea how to use them or how to accurately monitor them. Drag needle gauges make this task much easier and more reliable.
As for change outs I prefer not to let them go more than two years, regardless of how dirty they are. The filter paper can be degraded by any moisture in the fuel. I have seen a two filters blown out over the years and the owners never knew until the engine stopped. None of these were Racor filters but one of them was a Yanmar on-engine filter that had literally collapsed. I have no idea how long it had been in there but do know it had been at least the three plus years my neighbor owned the boat.
For our boat, with its polishing system, I will still change them at year two even though they will be perfectly clean. Filters are cheap and engines are expensive. The polishing filter will get changed at about 7-8 inHG of vacuum or every two years.
This drag needle gauge is from Sailors Solutions and made especially for them. It is a better drag needle gauge, quality wise, than the Racor with drag needle and it costs less money too. No need to be running at WOT under load to monitor your vacuum gauge as the drag needle stays at the highest vacuum sensed.