I have a problem with generic midi controller when it comes to using an arranger - it's not very ergonomic.

Arrangers require more button-pushes than the average keyboard. Using a midi controller is fine for selecting one sound at a time from a module but with an arranger you are required to select intros, verse, choruses, endings and trigger fills in addition to selecting sounds and layers... that's not so easy when the buttons are not on the same instrument you are playing.

Then again there are some stand-alone arranger boxes like the Roland DisCover 5m or the Yamaha QY700 that require you to use an external keyboard so it's certainly possible to do so, but I like having it all in one. And not all arranger keybeds are wacked, just some.