The CRAN version of bench is very stable. The dev version has the half finished continuous benchmarking code, which should either be extended or removed, see future directions for discussion.
Continuous benchmarking - feature development of this was largely derailed by COVID-19, I originally proposed it as a topic for a talk at UseR!2020, but when that conference went to virtual only it became less of a priority. In addition the ursa labs conbench package has provided a good alternative to what is done in the bench package (https://ursalabs.org/blog/announcing-conbench/) and https://github.com/ursacomputing/arrowbench.
Possible future directions would be talking more with the arrow team on bench features which would be useful for their use cases and extending bench functionality with them.