There are plenty of music streaming apps to choose from, but Amazon Prime Music is the only one that many people have already unknowingly paid for through their Amazon Prime subscription. In the way that Amazon Prime grants users access to a wide library of free films and TV shows, Prime also includes a music library. If you already pay for Amazon Prime, their music library comes at no added cost. Amazon Prime Music's library has 2 million songs ad-free. This is a significant advantage over other free music streaming services such as a basic (free) Spotify subscription which includes ads and limits how many songs you can skip. In addition to Amazon Prime Music being included with the Amazon Prime membership, members have the option to update their subscription to Amazon Music Unlimited at a discounted price. Amazon Music Unlimited is cheaper than other similar streaming services (Spotify Premium and Apple Music) for existing members because of this discount.  Amazon's music service offers the best value service to Prime Members who have automatic access to a small but free library and have the option to upgrade to the full 50 million song library at a discount. 
Amazon Prime Music comes at no extra cost to Prime members, but unless you pay extra for Amazon Music Unlimited, it grants access to a fraction of their music library. An Amazon Prime membership includes access to only 2 million out of Amazon's 50 million song library. For unlimited access to this collection, you'll still need to pay a subscription fee just like Spotify, Apple Music, and other streaming sites. Amazon Prime Music suffers the same drawbacks as Amazon Prime TV and Film in a way that offers a limited library.
[P1] Amazon Prime includes television, film, and music streaming. [P2] Amazon Prime Music comes at no added cost for Prime members. [P3] Amazon Prime offers the best value music streaming service.