I use Betterment, and love it. It's true that you can recreate the same experience with Vanguard. However, I simply do not feel comfortable re-balancing manually. Yes, I've been told that it isn't particularly challenging. I just feel more comfortable turning it over to a computer. In addition, Betterment helps me keep my 40 year outlook in perspective. I fear that if I were doing this stuff on my own, I would have a difficult time focusing.
In regard to Tax Loss Harvesting, I love it. It will have saved me more money this year than Betterment has cost me in fees.