Watch the Adding the Flat 9 online guitar lesson by Fareed Haque from Jazz Rock Workshop
You can use the b9 to move down to tonic OR up to the ii chord. The b9 is a sub tonic and musically can sound "ethnic."
In harmonic terms it can imply the b2 chord (for example, a Db7 in the key of C or C minor), but it can also imply the vi chord such as Am7 in the key of C.
So while the b9 can sound ethnic, it can also sound very melodic and "western" if used to move from a vi chord to a ii and then V chord progression. As always, it's important to add these notes in all positions.