In this paper we continue to examine various types of optical frequency combs (OFCs) obtained with frequency down-conversion method in a frequency-shifted feedback laser operating in mode-locking regime without an external optical seeding. We propose to apply these combs to solve several problems associated with the feedback loop length and, consequently, time delay variations -for example, distance measurements, determination of the optical materials refractive index value and dispersion. The advantages of OFCs application obtained by the sequential frequency down-conversion method (dual-and quad-combs) in comparison with the initial OFCs, the spectral interval between the lines of which is determined only by the delay time in the feedback circuit, have been demonstrated. The sensitivity of the examined system to the optical path variation in the feedback loop is determined.