Here's a real quick FAQ on what the buttons do as if you didn't already figure them out:
Simple enough
To get the app working, you’ll need an API key. You can get one by signing up for an account at Open AI
I assume people using these apps want the cool looking app and they are just too lazy to get a free key. So they pay $10/month for something they can do for free. But signing up for a key is hard and it's just easy to download some "ChatAppName" and do the same thing except:
At first yes, you get some credits to use it. Eventually you will pay as you go which is cents. That $10/month app you subscribe to do the same thing, you'd pay way way less if you just pasted your own key into this app and used it.
Check the Open AI Pricing for details but we're talking CENTS like .002 or .03 for 1k tokens (~750 words is token give or take)