That sensor available at Adafruit uses the same algorithm for calculating PM levels, it's literally the same chip. Maybe using 2 of them yields more accurate results though.
The Adafruit sensor is just the sensor, the PurpleAir II is two sensors plus extra logic that processes the readings to give extra accuracy.
You can't expect one sensor to give the same performance as two sensors plus correction logic. If it was that easy, PurpleAir could just put a case on a PMS sensor and be done with it.
The specs for particulate matter are identical:
https://www2.purpleair.com/collections/air-quality-sensors/p...
https://cdn-shop.adafruit.com/product-files/3686/plantower-p...