Padraig, Id agree with you. I have a garmin 740S on my Scarab and it is very easy to use (with what little I use it for). The only problem I ave had on my Scarab is the screen is small. On my new boat, (24' Sea Ray Flybridge), I wanted to try something different. I wanted something that has a bigger screen, and easier portability between using it on the top or bottom helm.

My biggest question is If I do not have cellular service to connect either an Ipad or an android device to, will the GPS still work?

from my experiance, yes...... as long as the ipad is cellular capable. If it is a WiFi only iPad it does not work well if at all...... but the service does not need to be hooked up. I was told that the ones that are cell ready have a gps inside and when I use my iPad pro for a gps it works great. I do not have it hooked up for service.....

So now the question really becomes Ipad or other tablet!

Ipad's with cellular capabilities will have an internal GPS, once you download the charts...you can go offline and use them and your boat will track via the internal GPS. If it's a wifi only Ipad, you won't have the GPS available when offline and it'll be useless to you. You can buy an optional GPS puck to use in conjunction with your ipad if you happen to not have the cellular type. I think the puck is around $100, which is usually the diff between the two ipad prices.

I used to use my iphone 6plus, but the screen is too hard to see when the boats on plane, ipad makes it much easier.