Heroku (and pretty much every PaaS) has features like this built in, and they tend to work really well... assuming you're using Heroku.

If you're using a PaaS that offers this, you (99.9% of the time) shouldn't look elsewhere. Just use their offering.

If you're not using an explicit PaaS, rebuilding this functionality yourself can end up being a never-ending rabbit hole.

You can use heroku, but as your app grows in complexity, (say static javascript frontend, backend, queue, and maybe a few AWS or GCP native services) you have to stitch something together with heroku + vercel + ?? + can't use RDS, but wish i could. :)

Heroku review apps are analogous to our ephemeral environments, but we can deal with much more complicated environments, which reduces complexity in your CI/CD platform, production deployments or on-premise deployments if needed.

Too expensive for larger deployments.

Also Heroku deployments are a PITA when you want fully (or partially) isolated environments but also work with a lot of microservices.

and this new thing won't be?