Operationally, both amps are very similar, however, internally the two are quite different.

A primary difference is that the BC-525D uses capacitive feedback circuitry in the headstage while the BC-535 is resistive feedback. 

A potential disadvantage with a capacitive-feedback headstage is an artifact commonly known as the 'reset glitch'. This is manifest as a small interruption in the output signal that occurs when the capacitor must be discharged as it approaches saturation. The reset glitch has an amplitude of approximately 1-2 pA and a duration of approximately 100 us. By comparison, there is no reset glitch in the BC-535 since it uses a resistance feedback headstage.  

Another difference is the maximum current each amp canhandle. The maximum current for the BC-535 is 20 nA while the BC-525D is limited to 200 pA. Furthermore, the BC-535 has a wider bandwidth, better gain (0.5-1000), and less noise than the BC-525D.