Spherical mirrors spectrometers can have significant astigmatism that is not corrected by Czerny-Turner design. Astigmatism means that a point at the entrance slit becomes a line at the imaging plane (on the detector). This results in the loss of light and increased scattering potential. Essentially, in case of oblique incidence, spherical mirror has different focus in sagittal and tangential planes. Astigmatism can be corrected using a cylindrical lens or torroid mirror. Torroid mirror is a cleaner but more expensive solution. This correction increases light collection  4x-5x. It also  decreases the coma across the spectrum – this is important for clean symmetrical peaks in spectroscopic data. 

CMOS detector response  is fairly linear at the low signals (<50% of dynamic range). But becomes non-linear at higher signals. The non-linearity is caused by the source- follower and charge to voltage converting capacitor. Hence, nonlinearity is slightly different from pixel to pixel. It is accurately corrected by factory calibration. The residual non-linearity is < 0.5%

Dark signal depends on integration time and temperature. For an active CMOS detector, each pixel has a bit different dark current with a different rate of change. Each spectrometer is carefully calibrated on  per pixel basis and for range of operating temperatures. This calibration is stored on board and automatically loaded depending on temperature of the detector. This way, the dark is fully corrected.