I'm assuming you are using CBC. In that case, the scaling of the None utility depends on how often the respondent uses the None. Sometimes, using the None truly represents that the respondent is less likely to choose (buy) something in the real world. But, sometimes using the None is more related to the positivity/negativity tendencies of the respondent when interacting with the survey. Sometimes the None usage is more related to the fatigue affecting the respondent. So, I get a bet nervous when trying to use the None to segment respondents into more or less likely to purchase groupings.
Zero-Centered Diffs scaling is just a normalized scaling of the raw utilities, where a multiplier is found to scale up the magnitude of the parameters so that the average difference between best and worst levels within attributes is 100, per person. So, the interpretation of the None vs. the sum of utilities for other concepts should be the same no matter whether using zero-centered diffs or the raw utilities.