This is not a one size fits all answer. Some motors burn oil and require topping off between oil changes, some don't, and some are in transition from not burning oil to requiring a top off. Which of the three does yours fall into? That will give you the answer.
As to the iDrive oil level tool, I trust it and use it. Over the past 13 years I have had four cars with it, three of which are still in the fleet, two of which have a dip stick for physical check. I use the iDrive method periodically if I happen to be BS'ing through the menus, other than that all my cars make it through a full oil cycle without a top off so not something I obsess about.