When Keystep's clock switches are set to "internal" and I set Ableton Live to use external clock it doesn't work very well.
First thing is this: when I turn "rate" knob a bit then it takes a long time for tempo in Ableton Live to settle - often it's like 30 seconds. It didn't harm me in practice so far - it's just minor annoyance.
What is more bothering is that when I turn the "rate" knob then the Ableton's tempo shows some value, say (real life example) 147 and then immediately after it goes down to say 122 which likely is the actual tempo and then it takes some more time to settle. Of course this upward swing to very high tempo is actually noticeable - metronome and all my sequences for a moment go way too fast and then immediately slow down. It's quite drastic and noticeable.