To my knowledge, they make money because they act like a credit card (they collect cc fee from the seller), but actually just proxy the charge to your bank account. You basically lose out on any your own cc rewards though since you can't proxy to another cc (then they would lose their profit margin paying your cc provider).
Personal example of when I found it useful:
I used a burner card from them to buy a board game online, turns out the site was hacked, leaked the card info, additional charges were attempted but failed because the burner card settings only allowed the original charge through. Was really glad I didn't use my own cc.
Just to add to the other comments made here, the NewUnboundedBuffer is meant to be a convenience method. It's actually just a (hopefully useful) example of how to compose the other buffer types to create a more complicated buffer. Thanks for the comment, hope it helps clear that up.
You've got the right idea. bytes.Buffer is great (I even use it under the hood) but this repo is intended to give you more control over how your buffer behaves as the amount of data stored in it changes.
The top results (click on the top Solutions) were pretty impressive: https://www.kaggle.com/competitions/drawing-with-llms/leader...