Given the cost of genuine map updates [AUD169 if you cannot get them free in service] and the extremely long periods between updates for the in-built media systems, in my opinion they are not worth it. My 2016 3.6 outback has all the bells and whistles including maps.
There are kits available to swap out the original radio and install after-market entertainment systems which could include a map system. They might be cost effective for the updates. Please look at the cost and frequency of map updates as these will be your biggest bugbear item. Most portable GPS Map units come with free updates.
My portable Garmin [now 5 years old] gets updates free of charge about every few months. The inbuilt system in the OB logs your journey but there is no way I have found to download that data for storage, while the Garmin can be saved by transfer to other media.
This, of course, predicates we are talking about map GPS unit for navigation and not about GPS tracking systems. That is a whole other field which I cannot provide an opinion.
PS I did not have the Garmin mounted on the windscreen but to a TomTom dash disk stuck to the edge of the dash