yes because they are made to fix a problem and part of the problem of porpoising is not being able to reach top end
most people get them because they have trouble get up on plane, therefor lower top end and lower fuel mileage and tabs will get it upon plane, so more speed and better mileage
however if you put them on a properly set up boat/motor, they will have lower top end..
again it is always better to fix a problem then mask it