I just double-checked and this still works for me on my iPhone using Dropbox to hold the html file. When I browse to that file in the Dropbox app and select it, it launches a web browser that works correctly. I am not sure why is doesn't work from google sites.
That said on my phone, I have completely switched over to use Siri Shortcuts to do things like this. You can set up a shortcut with your deviceID, token, and variable name and have Siri read the value to you, which has a high "wow" factor.