I've been upgrading my packages once a week for the last year without issue. Granted I am on an x86 which grants flexibility with filesystem type and size. I cannot recall a time when it has failed.
It is not bone stock either. I run AdguardHome, V-P-R with openvpn and Wireguard interfaces.
I have become more saavy with release upgrades (ex 19.07.1->19.07.2) and post install I am just about down to copy/pasting 3-4 lines via SSH and have my router fully restored post upgrade. One of these days I'll write a script and call it a day.