The display is a big one, ease of function underwater. For me I find the peregrine/perdix far easier and more functional when actually divingWhat "far better functionality" did you have in mind?
TBH in the past, I wished my Perdix had a stopwatch available in Dive mode like my Teric does. The Tag/Bookmark feature is pretty cool as well.
For the perdix, trimix and ability to integrate into ccr