Any $100 Garmin is far better than the factory navigation system. It has voice search, automatic internet updates and far more information available in it. Factory unit requires periodic expensive updates by CD. Not "built-in" which is a mixed blessing. It is not in your face with distraction when you don't need it.
My experience confirms the above recommendation. The navigation system that's integrated into the COMAND system in my 2004 CL500 looks beautiful, can be accessed in all sorts of convenient ways, but the first time I used it it proved to be so awkward that I used it exactly twice, then no more. Years later I upgraded the CD ROM for a couple of hundred dollars, and there was no improvement other than more modern maps. It still works but I don't use it. Rather than getting a Garmin unit I just used my phone's Google Maps, then Waze software. This is not a perfect solution because when I need to use the phone the navigation is temporarily interrupted. The Garmin is probably a better approach since it leaves the phone free. It would be terrific if M-B offered a useful navigation system like the one in my son's Tesla. But as far as I am aware it hasn't. Perhaps the current M-B car models finally have it.