The technician at Amel in Le Marin (the fellow that used to work with Jean Collin, has been there a while) talked me into buying a spare pump last year. The new pump looks nearly identical to the old one, same manufacturer. I have not used it yet.
We are currently cruising full time and the original pump gets a fair bit of run time. It runs for about 15 -30 seconds to drain the gray water sump. I'm not sure which Amel supplied pump you have, but the one that came with my SM (#37) has been good, except for the suction flapper valve becoming misaligned...which I finally fixed with a modification....don't tell Bill R.
Anyway the pump that came with my hull seems to be reliable, you might want to see if this version would fit with your layout.
Oh and Bill K is right, centrifugal pumps are sensitive to crud in the water. I would not rely on one as the primary water mover.
about to sail out of St. Augustine.