My understanding of the SPS30 data sheet is that the error for the category PM1/PM2.5 is +/- 5 for the full scale of the measurement (so for 100 micro g/m3) and +/- 25 for PM4/PM10 for the scale of 1000 micro g/m3. So the accuracy between two sensors is quite good (2,5 % and 5 %). Furthermore you may have the error induced by the rest of the electronics which may degrade this performance. That is why it is useful to calibrate the complete device with the data of official sensors installed in your town. To be accurate the calibration should be down for each sensor.