If your friend is happy with his Korg that's great. I would still regard it as an entry level arranger, albeit with a pro-level sound set. It doesn't have DIN MIDI jacks, or any provision to control the bass with organ-style foot pedals. I was disappointed to learn that Korg grouped "on bass" chord detection together with "Fingered 3" in a single menu setting, instead of making bass inversion a separate control as on the Pa700 and all of its older models. The result is that songs having mostly basic chords and the occasional slash chord are unnecessarily difficult to play, because ALL chords must be played with a minimum of 3 notes. (IMO Roland has the best system of this type; Casio comes close.)
Re: GO:Keys: I agree that the GO:Keys 3 and GO:Keys 5 are much more capable than the original GO:Keys. However, they lack any provision for "Sync Stop" (which silences the accompaniment when you release the keys.) Almost all arrangers since the 1990s have had this feature, and it's essential to my playing style. I have requested that it be added in a future OS update. In the meantime I would cross-shop the GO:Keys 3 against the Casio CT-S500. Download both manuals and compare them feature-for-feature. The Casio is also tidy and portable, IMO a good value in an entry-level arranger.