Yep! that is exactly what our system also does. QA sign off and automated tests run against our preview env. We aren't pushing PRs to prod.

It's just hard to justify the validity of a preview env if the deployment is different to that of prod, the deployment and infra is part of what you test IMO.

   The reality is that if you want fast builds an experience that makes it easy to compare different commits, etc.. there is a tradeoff.

What makes you say there needs to be a tradeoff? If you can deploy these preview environments so easily why can it not be the same for production too?

I actually think this is a great sounding product. I've pushed in almost every company I've worked at in the past to have per PR environments but never actually had it working for real until my current workplace and it is fantastic. It's for sure made easier with the use of serverless and/or container