Betterment is just a collection of tools, most of which can be found for free elsewhere, and they charge you for the convenience of having them in one place.
Automatic rebalancing:
1. you can use a Vanguard Lifestrategy or Target Retirement fund to do the same thing. Downside, great for IRAs, not for taxable.
2. this isn't a time intensive activity. Look at it once a quarter or even twice a year. Is everything close? Yes, leave it alone. No, then fix it.
Tax Loss harvesting:
If anything has ever been overhyped in the investing world it is this. Yes, it works, not disputing that. If you harvest your losses and then reinvest the tax savings(make sure you do that part!) then you have more money working for you. The problem is the results are normally inflated with rosy assumptions to make it look more appealing. Betterment for instance assumes you are a California resident(high state tax), in the 28% Federal tax bracket, and they assume you NEVER liquidate the account. That last assumption significantly inflates the results. When you harvest losses you are really harvesting your own cost basis. That means when you sell the holding in the future at a gain your capital gain is actually larger than it would have been if you hadn't used TLH.
Example. Buy at $100,000, after a 20% down market harvest at $80,000, reinvest the $3,000(20k*0.15%) you saved on taxes so you have $83,000 working for you, and 20 years later sell for $500,000. You pay taxes on $420,000 in gains instead of $400,000 in gains, which means you pay $3,000(20k*.15%) more in taxes upon sale.
If you eventually liquidate the account you still end up paying taxes on the gains. The real perk of TLH was that extra $3,000 working for you during that 20 years, but you paid Betterment 0.25% which on $100,000 is $250/year. At 8% growth $3,000 would generate an extra $240 a year in growth.
If you avoid the rosy assumptions like high state taxes, high personal taxes, and if you actually plan on spending the taxable account(which you should since you spend it in FIRE before IRAs) then TLH isn't as great as it appears. It is still good if you want to do it yourself(you can do this yourself!), but I don't think it alone is worth paying Betterment.
My other concern with TLH is what the IRS does with it long term. If you read the tax code on wash sales it uses the verbiage, "substantially identical," for determining if you get to realize losses. The spirit of the law it to prevent exactly what TLH does, realizing losses without changing the composition of the portfolio. This has traditionally been used to say you can't trade Apple stock for Apple stock and take the loss, but you could trade it for Microsoft stock. You also can't trade VTI for VTI and realize the loss. Betterment is basically taking the Vanguard 500 index and switching it for Schwab's 500 index. These securities aren't identical because they have different names and ticker symbols, but if the IRS decided to enforce "substantially identical" I wouldn't want to have to justify in court how two 500 index funds issued by different companies aren't "substantially identical." Conclusion: IMO the IRS could make this go away at any time based on their existing rules.