Have you really used google maps welshgas? I’ve used the 510 in a 180 se I briefly owned. I had to lick my finger each time to make the screen respond. I’ve the posh unit (discovery media?) in my T6, and in my opinion, google maps trashed them both for clarity, common sense and traffic accuracy. Also, Google knows my calander so I don’t even need to input the destinations. Yes you may get stuck planning a new route in a remote part of the country without data, but the OP already has his existing 510 to get him back to civilisation. Where there is no signal I tend to find their are few traffic jams!
No one is saying the inbuilt systems aren’t a marvel of our time compared to a paper road atlas and printing out directions from ‘Autoroute’, but the world has turned again.
Anyway, the OP was after advice about Dab and Bluetooth. Your solution gets him both for £1500+, I get him half way there for £25. His call.
Yes, with an iPhone 7 and an Huawei Android phone. Both worked after a fashion. No live data in the welsh valleys, but poor phone reception as well. Likewise in N Wales and along areas of the coast. Abroad we tried the iPhone. GPS signal lost in every tunnel and had to wait to regain position. Live data for maps etc worked as long as good signal otherwise but re-routing was laughable.
How many Updates of Firmware and Maps has your RNS510 had since 2013?
Screen works perfectly as a Touch Screen, even with a protective film on it. So the fact that your unit has failed you doesn't mean that ALL other RNS510 units are rubbish. In fact all it actually means is that your unit is damaged or you don't know how to update and use it properly.
And do include the cost of the Data Plan and Phone in your comparison of prices.
Built in Unit - Annual cost of 24/7 Data plan for a true comparison.
So based on my wifes iPhone 7 and Data Plan.
SatNav £1500 - Data Plan Only 24/7 £600/yr, so after 3 years you would have spent £1800 on Data.
I know you and others will say " but I have the Data already ", true but if you are using the phone for SatNav then you have NO option to a Data Plan and they don't tend to come down in price. Shop around for other plans- enough horror stories about that .
Each to his own and be happy with your own decision BUT don't go hammering others for their choice just because you cannot get on with yours.
I'm sure and expensive phone/data plan and App Connect is perfectly suitable for you, its just not for me as it doesn't perform as well as a built in unit properly maintained.