I’ve been a rust user of symbolica since 0.1 and it is insane how much nicer it is to use now.
Builder patterns for constructing replacement rules (and now evaluators!), macros for namespacing symbols, and now the call trait to fill in for callables in rust.
Not to mention the broad implementation of arithmetic on Atoms (the expression type of symbolica) with other std types and with symbols.
There is at least one benchmark on the main page https://gist.github.com/benruijl/3c53b1b0aea88b978ae609e7369.... And although it would be nice if it was open source, it is still a much nicer setup than Mathematica, as it is source available, (+ some parts are truely open source), is much faster, can be used in rust or python (so no obscure bundled language to learn), and the license lets you use one core for free (always).