Yes, definitely if you want to play streams on your Amiga or Mp3's, and what's more, doing other things while playing, a Mas player is a must. Grab one while you can, from AmigaKit.
What I do when I don't use the Mas is to convert the songs to aiff, then you can use Amplifier to listen them right. I use
Aiff MP3 Converter on my Pc, and you can convert them in a batch with a click very fast.