Social distancing mandates highly effective in reducing Covid-19 transmission

Does the fact the entire study is based on people that chose to "opt-in" to being monitored make the dataset somewhat useless?

I would draw a slightly different conclusion: if you want to be safe, you can choose to be safe

Duh. That was never in doubt.

The issues with distancing policies are late implementation and removing restrictions before the virus was beaten or vaccine was in sight.

If the policies have been implemented early (and we mostly knew everything there was to know early on) the number of casualties would be orders of magnitude less at least in countries that have relatively effective ability to police their population.