Also, 2 x 2.5Gbe, so if you have a > 1Gbit && <= 2.5Gbit connection, you can do line speed without having to resort to more complicated router on a stick configurations.
Besides that it has quite a bit better CPU (quad core rather than dual core), so if you do anything that cannot be hardware-offloaded (e.g. Cake), the performance will be better.
The OpenWrt has better hackability though. USB-C serial is very handy if you manage to mess up your configuration in a way you can't access the device (though LuCI have this features where it can revert changes if a change makes the router non-responsive to the user).
I currently use the Flint 2 as an AP, so I cannot easily test it. I tested it at some point, but it was far less than the 2.5Gbe line speed. I vaguely remember something like 700-800Mbit, but I might misremember, plus disabling hardware acceleration also disabled PPPoE offloading, so it might do better without PPPoE.
The other question is whether it is worth it. As far as I understand, the Filogic in the Flint 2 has hardware support for fq_codel. When doing buffer bloat tests with the waveform test, the score would always be A, whereas on the same connection a Fritz!Box 5590 Fiber would show pretty bad buffer bloat (grade D on the waveform test).
Besides that it has quite a bit better CPU (quad core rather than dual core), so if you do anything that cannot be hardware-offloaded (e.g. Cake), the performance will be better.
The OpenWrt has better hackability though. USB-C serial is very handy if you manage to mess up your configuration in a way you can't access the device (though LuCI have this features where it can revert changes if a change makes the router non-responsive to the user).