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Cerenkov radiation is emitted when v>c/n, where n is the refractive index.
Cerenkov angle:
cos δ = v_t/v = c/(vn) = 1/(βn)

At the threshold:
β_t=1/n
γ_t=n/√(n²-1)

Main drawback: modest light output. The energy loss due to ionization or excitation is two to three orders of magnitude higher than the energy lost in radiating Cherenkov light, in the energy range where photomultipliers can be used (a few eV, or about 400 nm wavelength).
Main advantage: directionality.