ND filters (non-graduated) are only helpful for digital stills in very limited circumstances. The only time one really needs to use a ND filter for stills is if they wish to control aperture or shutter
speed, while retaining the correct exposure.
Since the Mavic has no variable aperture, that situation can be immediately eliminated. Leaving us only with shutter speed. Using a ND filter is helpful when one wants to increase the shutter speed (exposure time), while retaining the correct exposure. This is helpful for longer exposure times, giving the photo a sense of "motion blur". If that's not the desired effect, then there's absolutely no reason to use a ND filter (unless you use a graduated filter).
At high noon, the Mavic may not be able to compensate for exposure with the lens pointed directly into the sun - but I've personally never tried since it's basically impossible (unless you're holding it in your hand). At sunset (or lower on the horizon), the Mavic is fully capable of compensating for the overexposed sun by decreasing the shutter speed and/or the ISO. There's no need to put another piece of glass between the sensor and the subject, that can only introduce glare, dust, imperfections and other problems, particularly when the lens is pointed into the sun.
The suggestion to underexpose vs. overexpose (to then compensate in post production) is a sound one. The suggestion to accomplish this (without the need for a long shutter speed) through the use of a ND filter instead of simply changing shutter speed/ISO is not. This is of course relevant only for stills, not video. But many folks appear to tout the need to use ND filters in still photos without understanding the reasoning behind them. As a Mavic owner, I wouldn't spend too much money and effort dealing with the usage of ND filters, getting caught up in the push to utilize an accessory, as they're only really useful for video during the middle of the day and even then, only in bright sunlight and at close range.