used psu

Hi, in this days i need to buy a new PSU. I have to decide if buy used (good brand) or new (bad brand). The news PSU that i can afford are: -Gigabyte PB500 500w -Sentey SNP550-HS 550w -Xfx P1-500B-XTFR 500w The used PSU that i am considering is the Seasonic S12ii-520 which has two sellers...