He's noting the irony of how punishing "your" (the developer's) margins are, vs how easily you hand your hard-fought cash over to the high-margin wealthfront.

> install an app ruining him/her?

it's a metaphor, imagining Wealthfront's fees as though it were the subscription fee for an app.

I think the first three paragraphs are supposed to appeal to Silicon Valley engineers. The idea is that a lot of {Facebook, Google, etc.} employees spend their day doing a task with negligible world impact and then put their paycheck into Wealthfront for investment/retirement.

The second para says it all:

"Should he beat the odds, he’ll then take your 70 cents and plow them into another app on his phone. This app will not only charge him every day for the rest of his life, but it also increased his fee last year by over a dollar a month."