I got this app because the EQ on Spotify wouldnt reduce the bass enough to sound good on the small speakers that came stock on my new car. I used this and was able to make all of my music sound way better on the standard speakers.
However, I only gave it four stars because it was a little tedious to have to sift through and then wait for all of my music to essentially re-download or "sync" as the app calls it. From what I noticed the app will not sync the music if the phone puts itself to sleep or auto locks, but I could be wrong on that.
Regardless, I would recommend this to anyone who needs a good EQ for Spotify, especially if they are faced with speakers that arent fantastic regularly. I think I already got my moneys worth from it.
Sammich326 about SpotEQ: Equalizer Bass Booster, v1.1.4