I have a zero fret on my Voyage Air (folding travel guitar). I love the zero fret. It plays awesome and I like the sound. I am not sure why most fretted instruments don’t go to it (maybe tradition). The action at the nut end is automatically optimal (assuming good frets). The one thing I could see happening is having to replace the zero fret due to wear, but that shouldn’t be a big deal.
There is a zeroglide company that makes nut replacements with a zero fret for the contact point. I haven’t tried those but they look good. I was going to get one to try on a beater, but my beater has been loaned out for a couple years: