I see many entries about Nik and Affinity and I would like to suggest the following two ideas.
No1. When you use NIK plugins with Photoshop and then go back to Photoshop it creates a new layer but when you do the same in Affinity it overwrites the original layer you sent into Nik plugins. Therefore it becomes a destructive editor - the simple workaround is to duplicate the layer in Affinity Photo before sending it into a NIK Plugin - this is fine unless you forget to do so. So it would be a good idea in my opinion to make the NIK plugin behave the same in Affinity as it does in Photoshop.
No2. When you go into the NIK plugin from Photoshop you get a brushes button at the bottom. When you do the same with Affinity you do not get this brushes button. It might be a good idea if this button was available when going into Affinity Photo.
I have used a licenced copy of the NIK plugins for many years firstly with Photoshop and for the past year with Affinity Photo - I have experienced no problems with all the NIK plugins when used with Affinity and I would be willing to purchase a new DxO licence if I new that these two features had been addressed.