Just had this issue with the sound (not midi) tracks where pressing a trig key then playing a key on the digitone keys keyboard would make a chord that included the default note for the track and the key pressed.
I noticed that this bug didn’t occur on the other tracks and it turned out that a power cycle solved the issue.
It is similar in that regard. Notes can only be programmed with the same length and velocity. I “think” when you use an external keyboard to record the MIDI data you get variable velocity and note length. I just don’t work that way so I can’t speak with certainty.
You do get double the polyphony though; 4 on OT VS. 8 on DN. OT gets MIDI Arp (very powerful) VS. no MIDI arp on any other Elektron device.