I’m not sure if this has been picked up on before (and I’m happy with my Garmin) but Ordnance Survey appear to be selling their own range of GPS devices (including a bike specific one) – https://www.ordnancesurvey.co.uk/shop/gps/os-gps-devices.html.

I don’t know if they’re something OS specific or just badged up an it’s not clear if they do turn by turn navigation or what map formats (beyond OS) they’ll take but they look interesting (if a bit spendy). I assume that the Velo has a sim socket as it does live (subscription service) tracking without a smartphone.

Do you have to keep paying a subscription, AND pay for map areas as you go?

I think that you can buy OS tiles on a one off basis but can subscribe to OS maps for £20 a year; the live tracking service does look like a recurring subscription service.