First off, this album isn't "new" music by Outkast. Rather, it is a collection from their various projects over the last few years (such as singles for sound tracks and songs where Andre and Antwan have been featured, many of which have different titles). Although is seems that Outkast has failed to promote this album at all, it appears to be a legitimate collection. I called Amazon directly and they explained that the Album is being sold directly by Amazon, and not a kid making Cd's in his basement (I hope).
As far as the content goes, this album contains the same great music the hip hop community has grown to love over the past 16 years. Lyrically, Outkast is great. The beats are excellent as well. The featured artists are all pretty good (Cee Lo Green is always great).
Overall, if you support Outkast and would like to do that financially, buy the album. Otherwise, sit back and wait for Dre's solo album followed up with another true Kast album.