I assume you refer to the presence of the Poly Blue?
The Plethora has the sub n up, a harmoniser, and a pitch shift. In short there isn't much it can't do octave wise.
However...the MXR Poly Blue is just my favourite pedal. Honestly there's so much it can do. And it's so easy to adjust on the fly.
It's overkill having so many options but I like simplicity, and the Plethora is a simple way to have 5 pedals in a small space. It can do so much more of course but it handles my modulation and compression needs admirably.