Cycle.travel app instead of Garmin devices?

Hi there,

I use cycle.travel to plot routes and send them to Garmin Connect and onto my 840 and 965 Garmin devices for navigation. I have prepared a whole cycle tour starting next Sunday and I am thinking that if I relied on Garmin for navigation I’d be totally lost because today Garmin has had a world meltdown on certain devices like my 965. 

I have the cycle.travel app on my phone and it allows you to download maps. When you have the map on your phone does cycle.travel need cell data to work or does it work from gps like Navmi does. I only have 12gb allowance from my network for my trip so I’d be concerned it would max out if I was using data for navigation. 

Does anyone know if it uses gps or data?

Thanks

Tom

Is this the symbol for a mountain refuge?