Is it one of those combined nuts and zero frets like this?
https://goldtonemusicgroup.com/zeroglide/
Just looking at pictures them and the zero fret doesn't seem well supported on the headstock side of the fret. They would look to need a lot of fine tuning to get everything to fit the fret in the same way a real zero fret would fit.
I've seen reports of them not working very well. I think someone on here tried one recently and wasn't impressed and went back to a standard nut.
Also an old thread here: https://www.buildyourownguitar.com.a...ight=zeroglide