As mentioned, if they're working fine, I wouldn't mess with it.
That said, I have found that in my implementation, the Zigbee locks seem to perform better than the Z-Wave. (Same physical lock shell, same (perhaps obviously) hub location, just a different radio card.) Of course, one's experience between the two will vary from everyone else's just due to things like repeater locations and overall mesh health. For me, I went from ~1/week missed status updates on Z-Wave to ~2-3/year on Zigbee.
If you want to go down that rabbit hole, this thread is a good place to start:
I think all of my Zigbee cards have come from Amazon (via Convert locks,) but you can find the cards themselves on eBay, too. (If you look at cards, look for 450201 or 450202 part numbers.
(450203 is compatible, but has a weird quirk I have not yet been able to investigate fully.) Just make sure you don't get a Control4 card.)
