What's the difference/the benefits in connecting to Google Analytics using Google's own connector, or using the Supermetrics one?
the main differences are that you can get more that 10 000 rows of data with Supermetrics connector, and that you can avoid data sampling. Other differences come from the usability. Feel free to test our connector by installing it from here.
Is there any way to indicate in within data studio doc if the data has come in as sampled?
sorry I thought that you we're talking about Supermetrics for Google Drive. Unfortunately it's not possible (at least yet) to avoid sampling with our Data Studio connector.
Please note that the data pulled in with Supermetrics for Google Drive can be also used within Data Studio.