I would offer some advice:
This month I earned the Torb and Lucio skins by watching Contenders from my phone.
However, you could probably use any device. I would setup an older smartphone or a tablet with chrome, make sure its fully up to date, close out any apps, plug it in to power, log in on the site and watch the stream on it. Make sure the sound is up enough at least to not be muted.
Then you can run it full screen. But be prepared to check on it after every match or before a match to be SURE the Green Dot is lit up. If it isn’t, refresh the page and restart the video. If you choose to not run in full screen (so you can see the dot) then be sure to set the device screen timeout to be as long as possible or to never turn off. Some devices will time out if you aren’t full screen. Some devices may log you out if you don’t touch them for a long period, which is why I suggest checking to ensure you are logged in and have a green dot every so often, or at least every match that day.