The internal Flash memory is way faster, than the SD-Card slot. I also got the Sandisk SDXC 64GB Class 10 UHS-1, which is able to read up to 80-90MB/s and write just below 50MB/s. In my BV8000 Pro it reaches 53MB/s read and merely 25MB/s write. The internal storage reaches 132/190 (r/w, yes, writing is faster than reading).
So, 50MB/s should be enough for reading a few pictures, but as I've seen, there's also a Sandisk SDXC 64GB Card which is named exactly the same (including Class 10, UHS-1), but is considerably slower. Maybe the shop put in false information, but if it's real, you might have one of those only capable of reading up to 30MB/s.
Mind, that you also get thumbs from videos you took. This might take more time to make a thumbnail than for a picture.
As for the SOS Button, I'd wish for the same. You could download and install a PTT app, but the button only works as a shortcut to open the app. No walkie-talkie like behaviour, because then you start the SOS mode. It should be configurable: Those who need it, can link to the SOS function, those who don't need that, use it for something else, or nothing at all.
Expecially while taking photos, I accidentially activate the button, because my right tumb is right were the button is, when I hold the phone in portrait position.