There isn't any, its an unsubstantiated claim - firstly its a decoupling cap, secondly its used at a fixed DC voltage, so why would you need bipolar?
Read Cyril Bateman's capacitor articles on Linear Audio. Bipolar caps are preferred even in power supply applications. My Dac, Preamp, and Phono stages have only 24 N and 56 NX bipolar Blackgates as local power supply bypasses - all direct coupled jfet/Fet solid state, even the regulators are jfet/ Fet shunts with BG bipolars bypassing the LED voltage references. The power amp has over 90,000 uf of Blackgate including 4 of the 2,200 uf/100 V N series bipolars - one on each rail.
