What benefits do you see with paying Betterment's 0.25% annual fee?
You can't use tax loss harvesting in an IRA or 401(k) account. If you want simple handling on automatic, without thinking about it, you can buy a target date fund (Vanguard, Fidelity, Schwab all have them). Those funds include U.S. stocks, international stocks, and bond allocations.
I suspect you could buy "Vanguard Target Retirement 2025" (or 2030) and have everything handled for you for a lower fee.