I installed my own garmin gps in my car about 10 yrs ago when I bought the car, new. I did a very custom install and people are usually impressed by it. its also quite hidden, which is why its not been taken OUT of my car in 10 yrs.
but now, 10 yrs later, the maps are very out of date for many areas I drive in (bay area). I'm too cheap to buy an update and so I use my android phone. it sits in a center cup holder area, it uses cellphone locations and gps and always stays current, for free.
I don't love google, believe me, but I'm not sure I'm willing to go back to old school gps boxes again. I also can't see paying the car co for their version when a cellphone does gps these days just fine.
if I had garmin stock, I'd sell it. same for others. they were great when they were all you could get; but now smartphones have this one killer app and that's gps, for many of us. I value the gps almost more than I value remote email and web on the phone.