Tried upgrading to this version from QTS 5.2.9.3451, and got a big warning screen from QTS thinking I’m attempting a firmware downgrade.
I didn’t have this issue when upgrading from QTS 5.2.9.3499
I guess QNAP hadn’t yet updated their version check routines to handle ‘10’ as a minor version number in build 3451. 
Update: looks like this problem was fixed in build 3492, as an upgrade from that build doesn’t show a firmware downgrade warning.