"The devices will arrive next week"
That is the simple future, and it impliess the devices will arrive all at once in a single shipment.
"The devices will be arriving next week"
Here you are using the Future continuous as you must use the -ing version. The meaning is a little different as it implies a continuous action, so the devices may arrive one by one each day.
Often the difference between these two tenses is ignored in speech. Both of these would be used by native speakers but I would prefer the Future Simple unless I wanted to emphasize the different arrival dates.