> agree to it to use the software

There's no "meeting of minds" and there's no exchange of value if I simply benchmark a piece of software and then don't use it any further.

This is a bit of a grey zone legally, and steps all over a bunch of consumer protection laws, free speech laws, etc... depending on the jurisdiction.

IMHO governments should explicitly ban these "gag clauses" because it prevents free market competition if customers are not allowed to benchmark software and publish the results.