This is great news. One limitation with Lets Encrypt is their rate limits are a bit low for Review Apps - you can’t issue more than 50 certs a week under a given domain.

So if you’re spinning up tens or hundreds of review apps per day, you can’t get a fresh cert for each, and so you need to do something different than your production environment does. (A wildcard cert is the obvious choice.)

I hope this offering has a high enough quota that you can get enough certs to do review apps properly; the marginal cost to Google per customer is probably negligible, whereas LetsEncrypt doesn’t have other revenue generating offerings they can use to cover their operating costs.