I have both, the main benefit of the Keystep Pro in my setup is as a compact master keyboard I can use to play into four devices. The Digitone is one of them, and this probably an obvious point but Digitone opens a lot when you actually use a keyboard with it. I sometimes use the Keystep Pro sequencer as a staging ground for a sequence I will then record into Digitone to edit with all the Elektron tricks. This is mainly just because it’s right where my hands are that are playing the sequence, so it’s more about ergonomics than anything.
I don’t think the Keystep Pro sequencer is particularly special in of itself, especially compared to an Elektron sequencer. For Eurorack it’s convenient, but you’re really just getting 1v/Oct + gates (and velocity, but that’s of marginal use as a modulation source for my system, ymmv). It doesn’t compare to having a full featured MIDI to CV device (eg. FH-2 or CV.OCD) and sequencing CV via CC control on an Elektron box with plocks etc. You do have the ‘Control track’ which can do something similar to plocking CC values, but the workflow is pretty awkward compared to an Elektron device.
Not exactly - you’ve got 4 MIDI tracks on Digitone, and 4 ‘tracks’ on Keystep Pro, which can go over MIDI and/or CV. You could have one track sending note data to both a MIDI device and a Eurorack module at the same time, but they have to share the pattern data. Track 1 of Keystep Pro can be a drum sequencer with 24 lanes instead (i.e. it is an either or situation), but I’m not sure you’d necessarily see them as separate ‘tracks’ when you were actually using it (you could split the drum sequencer so 8 notes go to the CV gate outputs, and the rest to a MIDI channel, which could then feel like 2 tracks).
One thing I like about it is for me it’s connected to the Octatrack which goes to a bunch of other things, and the way it handles polyphony is FAR FAR FAR superior to Octatrack’s sequencer, which is incredibly limited, so I’ve found it handy for that. Digitone’s handling of polyphonic sequencing is pretty good though. If you’ve just got Digitone, you have no MIDI arp so that can be a benefit too (less so for me with the Octatrack), I don’t find the Keystep Pro arp to be superior to the Digitone’s for controlling Digitone itself though.
tl;dr - if you’re buying this primarily for the sequencer, and not for the package of keys with a nice bonus sequencer, there are probably better options you can get. But it’s a very handy package if you need some keys and have a few bits of hardware you want to play from one device, I find it incredibly useful for that.
This is a very nice benefit KSP has.