Long ago, I have decided not to recommend a product whose manuals you couldn't see before buying it. It came from a huge disappointment over ATG's Dynamo web platform that led to a cancelled project and some lawyering. If we could have seen all the documentation, we'd have decided against it.

Benchmarking is the same - unless I can see independent benchmarks (ones not authorized or paid for the software maker, done based on publicly available knowledge on the platform) I'm not buying.