I haven't had a phosphate problem with my sps tank, so haven't really really looked into phosphate "reactors"
My opinion is that once you remove the source, whether it be water supply, food, dsb or live rock leaching old nutrients, etc., and then remove available phosphate in the water column through rowaphos, etc, you should not have to run this all the time.
Most SPS keepers also run large refugiums, this should keep phosphate in check over the long run after removing most of the phosphate through a phosphate removing product.
All in all, I don't see PO4 sponges being run 24/7 for a long time.
JMO.
Plus they are expensive to run 24/7 in the long run. A jar of Rowaphos is ridcously expensive.
Mike