Both HPLC and GC require a cannabis sample to be dissolved in liquid solvent(s) to strip away the non-cannabinoid substances, then this liquid is pushed through small tubes until an optical sensor records the amount of cannabinoid. Both techniques require continual calibration and cleaning, which necessitate trained operators. Between the cost of the instruments, the solvents, calibration materials, and the personnel, these techniques run well into the tens of thousands of dollars to set up and operate.
The Purpl PRO uses light to measure a ground sample directly, comes with its own calibration module that is indefinitely reusable and done once-per-week, and is usable by anyone. It also fits in a pocket, costs $1,495, and leaves the sample usable after measuring.