I'm hoping this Summary of what I've learned in research over recent days about iOS apps vs GPS vs maps use in Europe-France may end up useful to some folks who visit this site. It's by no means thorough:
First it's useful to know if your main need will be cities, countryside, and/or country-wide trip planning ahead of time.
Also, will you be driving solo or with a copilot? As I've said, my solo driver needs are for voice guidance. And I need a whole country available for pre-trip planning so I can enter villages and towns I want to go to into the 'destinations' before leaving. Then I can easily pull directions to them up on the run.
App solutions for iPhone or iPad or Tablet (Maps.me, Google Maps, CityMaps2Go etc) can provide country maps to download offline for free. These can then be referred to by the copilot as you drive, assuming the device you're using has the memory needed. When in a city or generally urban area, Apps use cell towers and limit your immediate access to 'zones' (the parameters of which I don't yet understand). They generally do not provide voice instructions.
In the GPS world, the main contenders are Tom Tom, an English product with more European users, and Garmin, with a more US & North America user base. These user bases affect the quantity and quality of the feedback you get on reviews for either brand. City traffic is the big popular item for Garmin users. It's hard to find reference to overseas travel on Garmin reviews.
GPS seems better for backroad driving because it uses satellites instead of cell towers which are farther apart in the countryside.
I called Tom Tom because I have an old XXL unit and I wanted to understand options for updating. First, I confirmed that indeed, the prior iOS App Tom Tom had for iPhones, iPads, etc, was discontinued (presumably the one getting all the bad reviews Roz linked to), and it has been replaced with a new one. I was unable (yet) to find reviews specific to that new iOS App software from Tom Tom.
I was told that the best option for me would be their latest updated 'VIA 1505M', which includes all of North America and Europe, and theoretically* ensures updates for life. These units have a slot for a mini SD card, which if 16 or 32 GB's, will allow one to switch between North America and Europe. Without the SD, one has to go into Settings and choose which set of maps to access. This unit is presently $178 on Amazon, $200 from TT directly.
After hours reading mixed reviews, my takeaway is that buyers with forethought and pre-planning found this VIA 1505M TT unit great for Europe. The bad reviews seem to come from either faulty units or impulsive buyers who don't read descriptions carefully, or don't do due diligence research ahead of time, or make assumptions from descriptions which don't really make sense. TT customer service responded to all negative reviews there, some with helpful info.
To buy only France for my old XXL unit from TT would cost $70. Given the improved touch technology on this 2016 made VIA unit, I'm tempted to go with it. If anyone knows more, please advise.
The gist is that the newer technology can be buggy, flawed, with increasing quality control problems
*'Free Lifetime Updates' is a controversial subject, and TT (not sure about Garmin) has promised updates it has not provided. Apparently new purchases with that guarantee are said to come with written documentation as to the lifetime update provision, but I need to pin that down.