For an M3W - For a closed/rental car ?

Is there a reason you would spend money on an external unit and not just get a local pay as you go SIM in a spare handset and use Waze/Google maps ?
Data only SIM's are available at LHR from the big vending machines and are £20 for a month of unlimited.

Reasonable review here if it helps. https://www.autoexpress.co.uk/product-group-tests/63573/best-sat-nav-apps-2022

If you are worried about data use there are map programs that do not use data and can pre-load specific maps over wifi in the hotel. Google maps does offer a pre-cache option but I get nervous about having to re-route on those!

Google bought Waze some time back and both use the same engine and data feeds. Waze is more about traffic and GoogMaps is more about whats around you etc. Both give great real time redirection.

EU SIM's allow roaming through Europe but are starting to cut out free UK roaming now and vice versa.

Happy to help if you need something specific. I use my iPhone and Waze from UK across FR, BE, NL quite often and it is perfect. It mixes in to the Bluetooth music and so I still get instructions over the dodgy Abba tracks 8)

Everyone loves a Morgan. Even me, unless it's broken again.