I've only ever owned "one" Kydex sheath...and will "NEVER" own another! Scratches the hell out of the blade, hilt, etc... I have a couple of nylon sheath, one that ,"was/used-ta-be", supplied by the Randall shop for their Divers knife.
No issues, thus far..."BUT"...(Ya' know that was coming)...a waxed sheath from the Randall/Sullivans shop fits my needs quite well.
Caveat Emptor,
Capt. Chris
PS: I even had a Kydex built, with "lining" that I was unhappy with...(I guess that means I've only ever owned "two"...)CCS

The reasons to "maybe" have a Kydex sheath.

!. Possible versatility in carry options. That is subjective with the individual and depends on needs.

2. Durability compared to leather if in high humidity/wet conditions.

3. Thin profile compared to leather. Often not as bulky as leather.

But...how happy a user is with a particular sheath depends on how well they understand and can communicate their needs/wants to the maker, and how well the maker can make a sheath that meets customer expectations.

Mentioning Mike Sastre in an above post...

He was partial to making a "Southern Comfort" style sheath with a slip-fit for a large knife. He did that for a 12-9 RMK...even though I told him I wanted a secure fit with a keeper strap...he was disappointed I did not like the result, eventually took the sheath back to "correct" it, and kept it until he died. (No, I did not want to carry a 12-9 stuck inside the waistband middle of the back, even if it was a slip-fit sheath and quick to deploy!)

Larry

Example of a Kydex sheath...The maker was set up at a show, and made the sheath there.

Larry

Looks great!

One of my PA friends also makes sheaths from kydex from time to time
https://www.candlepowerforums.com/threads/kydex-work-for-a-new-knife.485403/