On the one hand, theres a really big streaming song catalog; on the other, its not organized in a useful way, and most are old, cheesy-sounding, low-quality backing tracks. The key adjustment is nice, but with no volume adjustment for the vocals/backing, you might have to scream to be heard if youre using your iPhone mike. Newer apps (with more limited catalogs) have much better sound controls.
Sarabarra about Karaoke Anywhere