From a user point of view I feel like low,middle,high is sensible, but then I also see that being a minefield of bug reports saying 'low is too high', etc. I think in a lot of cases it might be something that needs just a 10-20% tweak to work better.
I think maybe as setOptions says accelerations are used they are in internal units, where 8192 = 1g, we could make twistThreshold measured in g, and adjustable by 0.01g? It then makes it pretty easy to tweak from the default of 0.1, and hopefully not too scary :)
Also if a lot of people find that one setting is better, it would be easy to translate that into values that could be fed back into Espruino's defaults :)