The NAV system in my 2016.5 CX-5 GT hasn't fouled up badly yet. Not sent me into dangerous spots, not into ditches or swamps, not onto dirt trails or "roads" where it imagines there's actually pavement.
Of course, in "country" road settings, it'll occasionally not have a clue of where to go. A few times each year I head to some places out there, so for those I just memorize all the correct turns. Easily done. But in well-traveled areas, it's generally pretty good.
One failing: it doesn't hardly notify soon enough. Often, if moving along at, say, 45mph, it'll warn me of an upcoming turn at 1000ft (or, when it thinks it's 1000ft to the turn) ... but actually the warning occurs just a dozen or so yards prior to the mark. Which sort of kills it, for making the turn (let alone making it safely). Doesn't happen all that often, but it's frequent enough to be a pain.
Had one particular spot that was a recent built-up along the highway, adding in a newer off-ramp. Turns out, that got constructed following the 2015/2016 time period when the vehicle got made. A simple update to the NAV maps corrected that little problem, which is to be expected.