Well, either the middleman at Digitec is already much more expensive than GoPro itself, or Digitec follows the Swiss competition and shows you how much margin there is on the product. It costs a similar amount everywhere. By the way, if you are a GroPro Plus member, the battery is 30% cheaper at GoPro, around CHF 14.
My experience is that you can have the unit in operation for max. one hour. During this time you can record about 20 minutes. Of course, if you turn the unit off in between, it will last longer.
Hello, I cross-charge with both and it all goes without a hitch. Unfortunately, I can't say whether this ultimately affects the batteries. I haven't had any problems with it so far.
Yes, the new 8-series batteries can deliver more energy for boost mode, which is why the old 6 to 7-series batteries simply work without boost mode in the 8-series.