I'm not against using QR codes. I just didn't realize that I could close the modal window, and thought that I had to jump through hoops to try out Sketch.
Given the amount of crap that can be found on the internet, I have a very low threshold for losing interest.
A better approach would have been to remind me later than I can scan a QR code to access the page on my mobile device.
The thing is that you need the Expo app on your phone to even try it out. Just closing the modal will show you the code but nothing else unless you installed the app and scanned the QR code.
I understand your point though. I suppose they can improve it.
1. People want to preview the app once they have something to preview. That would probably be a more appropriate time to remind them they can see it on their phones.
2. QR codes are scary (at least for most in the American market; other countries could be different). Instead of a QR code, show a random string the user has to input. We are all used to inputting random numbers/string when doing 2-factor.
1. The point of this is it happens in real time. It starts setup with an actual working demo. Connecting it to your phone first shows that real time update
2. This is an app for developers. Developers are not scared of QR codes.