I have never had any trouble with it. And there are dozens just like it on the play store. Free music download and mp3 music download pro are two examples. And the ads are no more invasive than the Go Launcher ads...they're banners and only exist on the app itself.
Samsung Galaxy Precedent (rooted, AreaRom 3.4 , sd-ext w/ 3.65GB internal space)
Kindle Fire (1st Gen, rooted, AOKP JB 4.1, Nova Launcher)
Samsung Galaxy SIII 4G LTE (rooted, Carbon ROM)