I see a new 6th edition came out in December 2017 Are the new editions worth it? My library lets me get an e-book of the 4th edition from 2007 for free, so are

I see a new 6th edition came out in December 2017 Are the new editions worth it? My library lets me get an e-book of the 4th edition from 2007 for free, so are the last decade of added material worth buying it?