I don’t honestly think that 2 years is a meaningful time span to measure how a tech changes people’s lives. It is certainly better than a single snapshot, but some effects take time to manifest - it’s simple behaviourism. More changes require more repetitions.
Edit:
> Second, we had objective measures of Facebook use, pulled directly from participants’ Facebook accounts, rather than measures based on a person’s self-report.
What about twitter, Instagram, and whatever else people use?
This study design also cannot show causation, just correlation. The control group is self selecting