GPS device for Loire Valley

You can’t go wrong with Garmin. I bought mine from my employer when they upgraded to newer models in our work trucks. It’s an older model, and the screen is small. I would suggest a larger screen.

I picked up a World sim card from Amazon rather than a country specific sim each time we travel.

Have you checked prices with Autoeurope? Usually their prices are very competitive. At least 5 years ago when I rented from Autoeurope I rented a GPS directly from them that comes preloaded for what is needed for your destination. They mailed it to my home and when we returned, I mailed it back. It was less expensive than other sources and It worked well.

The first time we rented a car in Europe, we did Alsace to Burgundy to Loire and then returned the car at St. Pierre de Corps. We used paper maps. Loire was quite easy to navigate and we never wished for GPS. That said, when we rent a car these days, I use maps.me on my phone. I download the maps when I have wifi and then the app works offline, the same as a GPS. It is free. We've used Maps.me for offline step by step driving directions in France, Spain and Sicily. I also use it for walking directions. I pin all my hotels, museums,restaurants, etc. prior to leaving home. Sometimes maps.me cannot find something and then I use Apple maps or Google to help me find it and then go back and pin it on maps.me. We always still have a paper map.

Use your phone and organic maps. No need to have a standalone device

For simplicity, I would just go with a phone - Google Maps, or Maps.me if you need offline directions. Since you won't be driving alone, you'll have a "co-pilot" and won't need the larger screen of a dedicated GPS device.
Directional signage is really very good in France, good enough to serve as a backup in most cases. Thanks to that, I very rarely use GPS while driving across the country (only Waze from time to time, but not for the directions themselves, more for when I want to be warned of speed cameras, or when I drive through traffic-prone areas).
And a paper map of the Loire Valley can't hurt - easily found at, for example, the newsstand(s)/bookstore(s) at St Pierre des Corps station.

Google maps or Waze. Likely they will plug in to the USB port on the Dash and display on the media center - and direct you in English if selected. Took my trust Garmin to Italy this spring, will not take again. 2nd day went to Waze and and never looked back.

Thank you all for your input...I know that Google Maps is pretty reliable so maybe we'll just go with that! I think Garmin was what we used before and it was a good choice.

Google maps is anything but reliable, unfortunately. It's ok as long as you're sticking to highways built more than 5 years ago, but the updates are dreadful (if done at all), and the routing is haphazard.

The reason OSM (most of the non google aps) is so much better is that they are updated every month, and in France that usually comprises information provided by local government - so even public toilet info, post boxe location, even park benches and trash cans - tend to be located accurately and the info is up to date (for instance, my local council uses OSM data for keeping track of its assets)

Chose the right flavour of ap and you may actually be able to see the map rather than your screen being covered in ads, as well

Also, just a sidenote for those interested--I personally rely on the Citymapper app on my phone for directions for myriad modes of transportation (walking, metro, taxi, bus) when in major cities. As Jules does with maps.me I plug in and save all my destinations before going on our trip and voila, it couldn't be easier. I really like how this app tells you in real time how long it will take to get somewhere, and also factors in any delays/construction/unforeseen hurdles and re-routes you to the most efficient means of transport. I tried maps.me in the past and for whatever reason couldn't figure out how to use it very well...this was awhile ago, so maybe they've made it more user-friendly. Citymapper for me was extremely friendly to use. Almost all major cities are represented (we'll use it in Paris), but outlying areas such as the Loire Valley are not available yet. They do keep adding locations all the time.

Thank you Simon for that input. Sorry, what is OSM?

Open Street Maps. So Organic maps, and Maps.me use Open Street Maps information.

I should also say - the contrast on Google Maps means you cant actually tell where the sterets are.

Thank you, I'll check it out!

Our last car rental in France was from Sixt in Paris. It was an Alfa Romeo with built in GPS. No charge and seemed to work. Preferred to use my trusty TomTom though.