Opinions on Acorns or Stash Apps?

Anyone use the app(s) Acorns or Stash? Long story short, it's an app you can use from your phone to help with investing low amounts ($5 min) into various investments, stocks, government bonds, etc. Consequently, they're a robo-investing app with little customization - as far as I've seen.

Do you guys use this? The round-up feature from Acorns seems kinda cool, but this is all opinion since I haven't really used it yet.