The -8 is perfectly fine to land with the AT on, it functions just like the 777.
The 400 will attempt to maintain SPD as said above, it will advance the thrust during the flare, if overridden manually to idle and the aircraft touches down there’s a rapid (1/2sec) mode change SPD to IDLE and immediate AT disconnection and the AT motors stop driving with associated master caution. Not worth the effort and distraction.
Unconfirmed reports that a update for the 400 AT to function as per -8/777 is available at a cost 💲