We are working on benchmarks comparing ourselves to other solutions so hopefully we'll have concrete numbers on those soon. (Incidentally, we did a blog post on us vs plain PostgreSQL today: https://blog.timescale.com/timescaledb-vs-6a696248104e)

At a high level though, we do find that having native support for full SQL to be a big win. Also, if you already store metadata or other relational data that you want to combine with your time-series data, it's great to be able to use one DB instead of separate solutions. Performance wise we do believe we are competitive and in some cases much better, and we have the 20 years of stability from PostgreSQL to build on.