This is wrong for a variety of reasons.

First, you should never accept angel investment from non-accredited investors (i.e., individuals with a net worth of at least one million cents).

Second, the real value of the investors is their network. In this case, Maciej Cegłowski's network is a collection of links featured in an indexed, polished, simple-to-use product. Why accept money from him when his network is already available for free?

Third, seeking outside investment prior to building a prototype has been heralded as a path to madness. You should at least have some sort of Bootstrap-based splash page on a .io domain before you accept his sizable investment.