* Render PR previews have built-in caching.
* Many of our customers use Preview Environments (currently in early access). For every PR, Render automatically spins up a complete testing environment including static sites, servers and databases that can be seeded with a hook. It's similar to Heroku's Review Apps, but a fraction of the cost.
* Render's Preview Environments are free for static sites and prorated by the second for servers and databases. Regarding pricing: we charge for actual usage (vs. a per-seat model) because previews (and consequently our own costs) rarely scale linearly with developer count.
More generally, it's great to see more activity in the space because it's a validation of our own product strategy, and there is obviously room for multiple players.