I've got one on my Jag-Stang, there may be marginally more sustain and brightness but only on open notes/chords. Once you fret the board the nut is cancelled out.
A fixed bridge like a TOM or string-thru is the best way to improve sustain, it has more connection with the body translating more resonance.
Have you tried a Boss CS-3 Compression/Sustainer?
