.25% on top of any investments you have through them, on top of the fund expense ratio https://www.betterment.com/pricing

That is 62k gone to fees assuming:

12k start, 12k put in per year. for 30 years at 7%.

People don't realise that the opportunity cost of those fees is compounding money.

In your example that 67k is 4.8% of your investments. And that's not including the fees of the ETF or mutual funds you get invested in.

I would never even think about touching this service - why would anyone use this?

Because it's easy. If someone's eyes glazes over before you get to the third Q in QQQ, and they're not going to entertain a conversation over Roth and 401k, some place to just money over to for retirement is very attractive.