There was a similar sub-discussion on the Datomic Cloud announcement last week: https://news.ycombinator.com/item?id=16168041#16168743

As an open source product it seems like TimescaleDB is less risky than Datomic. (Not that the comparison is even necessary -- I don't think they compete in the same category apart from both being non-relational DBs.)

[edit:link fixed, thanks! (and thanks for taking the time to correct my misunderstanding re:TimescaleDB as a relational DB)]