I use them every so often - usually run them along with carbon for a few days each month. No need to leave it in continously IMO, so you don't really have to worry about the mechanical filtration effect. They change color as they absorb stuff.
My opinion is that there must be a need for the filter. You don't blindly recommand filter-this and filter-that without knowing the specific demand for it.
I use polyfilters on my tank on occsassion as well, but only for short periods of time to "clean up" the water. They change colors as they absorb different compounds. Thus, I consider polyfilters more a chemical filter then a mechanical one (although it really is a "mechanical filter"). Bottom line is polyfilters work IME and are fine for reef tank usage. As Chris said, no need to run it continuous, but maybe once every other month for a week or so.
