And no doubt - you’ll still be laughing when your phone conks out in the heat of the south of France/Spain........
Not really seeing the worry about overloading your (yet to purchase) GS with an additional 200gm Sat Nav either
But - each to their own.
I've been taking bikes on trips to the South of France and Spain since before anyone had ever heard of SatNav or mobile phones (or the Internet for that matter) and yes, I did have a problem one year when the iPhone was packed in a waterproof case, surrounded by insulating foam. Otherwise I have used less 'encased' mountings and never had the problem again. With a modern waterproof phone that needs no case at all, I would certainly not expect to experience that problem.
I have also not experienced any other glitches when using phone based SatNav as opposed to a dedicated unit such as the TomTom Rider whose mount partially broke on the first day, repeatedly chose different routes to the same device my friend was also using (with same settings and route plan etc), insisted on sending me on the route I specifically was trying to avoid and generally pissed me off so much I nearly threw it into the nearest field. I didn't though and on my return sent it back as not fit for purpose and anyway, broken. Funnily enough, I've never experienced any such traumas when navigating with an iPhone.
As for overloading a GS with the extra weight due to carrying 2 devices, who said I was worried about that? Not the issue at all. Was that a dig about my not yet having purchased a new 1250? Your point is? If you wish to buy my car then you could assist me in more quickly obtaining the GS.
I first rode a bike abroad in 1973 and most years since. I've navigated using memory, paper maps, scribbled notes, dedicated SatNav devices and SatNav apps on an iPhone. From that experience I have determined that app on phone is by far the best solution. If you still wish to faff about with 2 devices where one will do, then that is your choice. But, it is important that everyone is aware of the fact that apart from being so much cheaper, navigation by phone does not restrict you to on-line maps that require constant downloading. Indeed you then have the choice of which app to use and can always change it at a later date if something better comes along or you simply fancy trying something different. A true SatNav app on a mobile device will give at least as good SatNav capability as any dedicated device. I am not alone in this realisation which is why the sales of dedicated devices has dropped through the floor.
Provided anyone making the decision has the full facts at their disposal, then it is their choice as to which device they use, but this choice should not be made based on any misunderstanding of the capabilities of phone based SatNav.