I prefer Arda to Epiccosplay. Epiccosplay wigs just seem too shiny and there is a lack of color variation in the wefts(all the wigs are one tone, idk how else to put it) though that wouldn't really matter as much if it were black haha. I think my Nep wig was a jaguar from Arda.
If you could cut it in such a way that you could use it for both characters, I would say go for it! I'm not sure how possible that would be though, given how much shorter Kanaya's hair is compared to Nepeta's.