I got these to replace the stock pickup on my American Special P Bass, primarily because I was getting a clicky sound every time my fingers made contact with the exposed pole pieces whilst playing.
The pole pieces are covered on these DiMarzio pickups, so that solved that problem. However, I also got an improvement in overall sound. There seems to be a bit more bottom end, not too much, just a bit more warmth maybe?; and the harmonics seem better too. They seem to have a slightly higher output than standard p bass pickups, but the P bass sound is still retained. I see these as a definite upgrade and would recommend them.