When you get answers from people with a vested interest, you need to beware what they write.

WebRTC is no different than any other media engine option out there. It is just as good and provides similar quality - sometimes better sometimes poorer. It is on par with other commercial media engine options.

There are two reasons for that:

  1. WebRTC's media engine started off as a commercial offering by GIPS, the company Google acquired. GIPS was used by many of the industry's top players, including Avaya, LifeSize and many others.
  2. It uses the same technologies as any other media engine. The only difference is in it being open source whereas others are closed source.

VP8, the current default video codec in WebRTC implementations is on par with H.264 for all intents and purposes. Opus, the mandatory voice codec in WebRTC is as good or better than the rest of the voice codecs implemented in other VoIP products.

Switching to solutions, it will be determined by the way the infrastructure has been laid out and the implementation itself. I know of no specific tool to objectively test quality of WebRTC products.
There is also a problem of comparing an on premise offering by a vendor to a service offering (SaaS) simply because quality will depend a lot on the data centers used and the way the systems have been configured.

There are many other aspects related to an implementation of a WebRTC service. I cover some of them in my report Choosing a WebRTC API Platform - BlogGeek.me (disclaimer: it is a paid report; overview can be downloaded freely).