I hope people realize Acorn's post is contrary to what Dave Ramsey tells
you to do. Those two things don't go hand in hand. If you go talk to Dave he'll send you to an "ELP" who will then sell you a loaded growth stock mutual fund that charges about 6% up front (of which Dave gets a cut) and has a high expense ratio.
Acorn is talking about simple cheap investing that only costs you a fraction of the cost compared to the crap Dave is trying to get you in to make a cut for himself.