This is a Digital Audio Player (basically a fancy iPod). These play higher quality files than an iPod or your phone can and/or sound better.
This one can play quite a lot of formats including a new one called MQA which has very small file size (though there isn't a lot of music available in that format yet) FLAC and DSD just to name a few. The other reason you may go for this one is it's based on Android (5.1.1) so you can install most android apps like Spotify and Tidal (it's basically like a phone without the phone function, but with boosted audio specs. It has 2 Micro SD slots and can take two 200Gb cards. This is quite big (about iPhone 5 size).
Another highly thought of one in this price range is the Cowon Plenue D US$199.25 A$247.98 (the silver one is cheaper than black and has just been reduced US$30).
This one has higher specs, but (from memory) is a closed OS so you can't install apps. It's more compact too.
https://www.amazon.com/Cowon-Plenue-Resolution-Music-Player/…
You'd really want to do heaps of research of different models before deciding which to buy as there is a huge range of prices and features. They have some limited internal storage, but you'd want to buy MicroSD cards as well for any quantity of music.
I was very interested in the Onkyo version of this, but found out that the EQ only works with the included music player and not with other apps like Spotify or Tidal. Pity!