If you have a smart phone, you can use is as a GPS (Google Maps) WITHOUT any hotspot, SIM card, or internet connection. It communicates with the satellites even when your phone is in airplane mode.
All you need to do is download the maps ahead of time - e.g. Google Maps "offline." Try it at home: download the map for where you live in Google Maps "offline" (go into "Settings" in Google maps to find it). Then put the phone in airplane mode. Then get driving directions, go for a drive, see how it works. It will work the same in Scotland, once you download the "offline" map for Scotland into Google Maps.
The biggest downside of Google Maps "offline" is: no traffic data. Just driving directions and maps. (And no walking or public transit directions - just driving directions.)
Renting a hotspot makes no sense unless your phone is locked and you cannot buy a SIM card - or your phone is really old and has no ability to work in Europe with European mobile frequencies. Or your carrier doesn't offer a cheap international roaming plan (e.g. if you are Canadian). I guess people with multiple devices using a lot of data might get good value out of a hotspot, but otherwise it would be more expensive than just buying a SIM card - and it means one more device to keep track of.