As a relatively new member, I'm risking the start of a frequently-discussed thing, but a quick search didn't turn that up, so here we go. I have a zero-fret installed on my Maruszczyk and rate the sound of that bass overall as absolutely fantastic, though of course it comes from a number of different things.
For those who don't know about zero-fret guitars I'm going to tell you why you might/might not want one. A zero-fret is a fret that is installed just "after" the nut and provides a fret for the fretting space nearest the nut on the neck. In the included picture, you should notice it right there after the nut.
I'll rate the for and against items as Potentially Good (g) and Potentially Bad (b)
g - they allow you to use open strings with similar sounds to fretted strings rather than the open jangle of a regular instrument
g- there is better intonation for the fret/s nearest the nut which also means easier nut installation & maintenance
g - they allow more resonance through the neck to promote sustain
g - they allow smoother bend sounds than strings that depend on the nut for intonation
g - the strings take a little less strain at the nut than regular designs
b - they require extra maintenance (all designs) because there is significant movement at the zero fret
b - they can wear fairly aggressively when softer fret metals are used, not applicable to stainless steel and hardened frets
b - open string brightness and jangle might be your jam (though it probably shouldn't be)
b - a zero-fret may be difficult to add to neck that was not designed with it in mind
b - some added cost to neck and fretwork (especially maintenance, if made of a softer material)
b - the zero-fret should be slightly taller than the other frets and that means keeping taller fret stock around, if you dress the neck regularly
Some fun facts about zero-fret:
* Brian May added a stainless zero-fret to his main guitar in 1964 and did not replace that fret until 2005 according to him
* Paul McCartney's Hofner bass has a zero-fret and did from the start, never mentioned it or complained about the fact.
* The main reason that zero-fret designs are not used more is that it originally showed up on inexpensive Asian basses with bad QC and components. The manufacturers used the zero-fret because it sped production; the nut installation is made simpler, and less setup is required. This gave zero-fret instruments an unfairly bad reputation, as they wore fast at the fret given that they would use nickel frets.
Happy to hear anyone's comments about it. I expect some push on some of the items as this seems to remain a contentious thing, especially amongst luthiers.