If you haven't heard of, or tried to use xip.io before, you'll know that device testing can be a pain! However, the team at Basecamp have setup xip.io which is a wildcard domain that you can use (for FREE!) to test a local site on multiple physical devices, as long as they are all on the same local network.
ServerAlias yourdomain.*.xip.io to the vhosts file, and you're ready to go! There is no other setup involved, you can just start using it!
The "*" in the alias should be replaced by the "server" internal IP address. So, for example, to access loc.drupal8site.com from my phone, I'd enter "loc.drupal8site.com.10.0.1.20.xip.io" in the address bar.
Since I haven't installed Drupal yet, I'm taken to the install page. I won't do it now, but you can see that it works!