I dunno...it seems pretty solid (although I am a little skeptical of them staying in business, but even if they shut down, it is easy enough to transfer funds out). No fees for the robo-investor service. Deals in fractional shares, so they can keep their ideal asset allocation even with small amounts of money. Doesn't give you a lot of control (but that's sort of the point), just fill out a survey, tweak your desired level of risk as necessary, and let them do their work.
As an early member, I got some of their tax loss harvesting service for free--and in the recent market volatility, it really does seem to have paid off. Downside is that you have to be really careful about what is being bought/sold in your other accounts. If they try to harvest losses on an S&P 500 fund, but you are inadvertently re-buying it in another account (like an automatic 401k purchase, or dividend reinvestment), you lose the benefit.
I set my GF up with it for her IRA, and I think it is a pretty good solution for that--turn on auto deposit, set a risk score, and then just let it go. Doesn't matter if you only deposit $50 a paycheck at first, because of the fractional share thing.