in my previous role we were migration several hundred frame circuits to an MPLS network. Once the circuit was provisioned from the provider we would peform our own stress test and turn up before moving in any users. This would include testing of through-put, load, stability, etc. Several times we would determine that our provider did not provision the circuit correctly. Also, during the same time, we would upgrade our existing circuits and we would never know when the provider completed the upgrade behind the scenes on our metro E deployments. From time to time we would also use it for troubleshooting.
Our security constantly would say speedtest.net was an invalid test, but no one could come up with a tool that had a "valid" test. We would have paid for one, and I am sure other would have and will also.