The interest of the scientific community in the use of synchrotron radiation has become higher and higher with the improvement of instrumentation and with publication of better and better results. For this reason, the concept of standard beamline could not be used anymore, and a lot of solutions must be considered to satisfy the requests of the different users. A very important part of these "solutions" involves mirrors, gratings and crystals adopted to carry out the light from the source to the experimental chamber. In the last years, for instance, we have seen an increased interest for the mechanically deformable mirrors, as well as normal incidence mirrors (for IR or UV photons). From the point of view of the optical metrology, this implies the use of different methods and different instruments to guarantee the quality of the optics and consequently of the delivered photons. In this work, we compare the performance of two "state of the art" instruments, aimed at the non-contact measuring of optical surface profiles. The first one is an in house modified version of the Long Trace Profiler (LTP) developed for grazing incidence optics by P.Z. Takacs and Al. The second is a Fizeau like interferometer (a WYKO RTI 4100), primarily used for 2D mapping of surfaces. The aim of this paper is to outline when, according to our experience, an instrument is preferable with respect to the other, what are the limits of both and what kind of improvement could be made. Some examples will be reported. Spatial frequency, calibration and systematic errors will be compared and outlined.