If this is to become a widespread product, I think it needs to address two linked issues: (a) the product appears to be tuned to the specific weight of an individual, so that the counterweights/springs are neutral in use. Changing between individuals (or changing weight should the individual gain/lose weight) should be easy to do and hopefully transparent. (b) the product can't be accessed if it is on a different floor. Without the weight of a user, if unlocked, it would skyrocket upwards. I don't want to lock into the paradigms of an elevator, but the user needs to be able to access the product even if another user moved it.
Unfortunately, the only thought I have to solve these issues is to electrify it, or perhaps a clever hydraulic system. In any case, I think with batteries, it need not consume power from the grid.