It's not cheaper, slower startup, we lose full control and the environment is not optimized to run Chromium, so we also lose performance

Cheaper by a factor of 2-5 depending on your usage. Read here: https://shellbox.dev/#post-race-to-the-bottom

Startup is fast, less than 2 seconds if you pool connections.

Also, what do you mean by optimized environment for chrome. You can use whatever image you want, use an optimized one if there is such thing