Hi,
We have been testing the PMS5003 in co-location with the SDS011 sensor and they give quite similar results in PM2.5 - PM10 values. Both sensors are based on a very similar principle (Light scattering sensor based on particule counting - more on this in some days in the docs).
You can see a comparison of the sensors in the image below for both metrics (R2 > 0.8).
It seems though, that the PM2.5 from a PMS5003 is a bit higher, but that is highly dependent on the internal math of the sensor. At the end of the day, what these two sensors do is just count particles that cover a laser beam. Then, with an estimate of the average particle density, shape factors and so on, they calculate volume and mass (PM). Each sensor could have different internal estimations and behave better with different types of particles, but generally, they correlate well (for example, the PMS5003 is said to correlate worse with particles coming from wildfire and better with other dusts and aerosols reference here).
Hope it helps!