Google App Engine (GAE) was cool because it was for free.
Then, Google started charging (really expensive), i got enough with it and i quit.
And you can trivially ensure you never exceed them simply by setting a $0 daily budget. (Although I recommend setting a low but non-zero cap instead, so your app doesn't go down if there's a legit but unexpected traffic surge.)
Disclaimer: I work at GCP.
I didn't register a card and all applications have been shut down. I will not register a card.
Basically, GAE cannot be used anymore for amateur, high school and student projects.
That said, I had once linked a card from my uncle with the private Google Wallet to buy a Nexus 7.
And yes, the CC requirements are insane. Every professional service supports SEPA transfers, except Google. It basically is an extra 30-60€ a year cost just to use Google services, or to develop for Google Play. 30€ CC cost plus 25$ registration fee. (CCs are basically unused in Germany, where I live).