I can't really explain how easy it is. There are no hidden charges, monthly usage is easy and clear to understand. For small to medium sized apps there isn't even any configuration. I'll be throwing tens of thousands of users, tiny I know, on a service that had 0 configuration done beyond typing its name. In fact I'm 100% sure my VMs on DO are going to give under load first.

To put it another way, there is a healthy industry of people whose sole job is to come in and figure out why AWS is billing too much.

FWIW I showed one of my friends at Amazon how easily I can create and deploy serverless code on Firebase, he admitted it is far easier than what AWS offers.

The downside of this is that options are fewer. If I want a beefier VM my choices are limited, and the way pooling and VM reuse is done is well documented and not at all under my control. It is like cloud on training wheels (TBF to gcp it is possible to opt-in to more complexity for many services, but the serverless function stuff is pretty bare bones on options, arguably as it should be)

But take auth for example. Firebase auth is amazing. Using it is beyond simple, and within the Google ecosystem everything just works so well.