Did you mean they said either sheath would fit either knife (interchange) ? I did not know this if this is what you mean, I have never tried this, if they will, no question I would choose kydex for either knife, it is a very tough sheath........what do you plan to use your knife for ?
The X-42 is a very serious looking knife.
It has a certain look and feel to it that you just have to see in person. Also be aware that the X-42 "TINI" finish will scratch under some circumstances, like course abrasives or any sharpening done with a diamond stone, other than this, it holds up well against normal cutting like ropes or any other semi-soft material like wood.
Both knives are two of the most comfortable I have ever held. (next to the Revolver
) The field knife sheath seems more subdued to me, it is a friction sheath and I read somewhere in a past thread that it held very well. You have to decide which knife/sheath you want by what you plan to do with it. I think each knife will perform well, but I also feel that each knife has it's own areas of expertise. IMO, the names of the knives pretty well describe what each knife was made for, you have to decide which is best for you.
Hope this helps.
Robbie Roberson
P.S. Heber is making some leather sheaths now that are amazing, you should consider one of these in the future for optional carry. I have about three I think, all are perfect.