On inertia: I totally believe that a fully physics based on would be irritating! (Also kudos for getting playtesting and then making design changes as a result). So if there was a scale from 0 (current) to full physics based (1), I’d shoot for like 0.1, so probably more like an extension of your current implementation of movement vs trying to introduce something new. Something that just makes the roll to a stop slightly slower.
On checkpoint: yup I totally get that rationale. Hm trying to remember, do you prompt the command + key to set the checkpoint when you are underneath it? I’d make sure at least that is done.
On the user prefs, I recall thinking “what do these numbers mean??” for a couple of the settings. So if you have that idea of making 2 = double smoothness, maybe you have a label off to the right which updated based on which “region” of the slider you are in to help reinforce the current position? Eg 1.5 to 2 makes the label say “extra smooth”. Either that or map everything from a 0-1 value, and have a small vertical tick to remind users where the default is?
Final thing… I forgot to mention in my first post, also really loved your little post-it notes and messages, great detail :) nice work again!