Just installed the bridge on my Squier Affinity P Bass. Tried it with my old nickel D'Addarios. Every ear is different so not all people can understand the effect of the Hi Mass bridge. But definitely it provides better sustain. Just record samples before and after the installation and see what you cannot hear.
The bridge was direct bolt on replacement, needed a bit of professional setup job though, as, even at the lower position of the saddles, the strings sat high enough to prevent you from setting the correct action. Also, the G string saddle needed a small alteration so that the string could sit exactly where it should above the pickups, aligned between the pickup poles. If it was a more expenssive bridge I would consider returning it, however, with some fiddling at no extra cost the problem was solved.
Overall I am very happy with my purchase, transformed my cheap daily player into a high quality looking and sounding bass.