Have a look at this:
https://matrix.org/docs/guides/free-small-matrix-server
But hosting a Beeper/Matrix server is not a no brainer!
On their homepage it says: _ iOS and Android via Element_.
That lets me assume that they either have a restyled fork of Element, or are directly telling us to use Element.
So yes, if you use Element (with any other matrix server, for example with matrix.org, you will see how the app looks like.