Hi Mihir, SAXS (small angle X-ray Scattering) ) is an instrument to be capable of delivering structural information of macromolecules between 5 and 25 nm, of repeat distances in partially ordered systems of up to 150 nm ( In fact, the sample is has inhomogeneities in the nm-range. Of course this instrument contains information about the shape and size of macromolecules, characteristic distances of partially ordered materials, pore sizes, and other data. So SAXS has a limitation to measure a higher macromolecules. However, surface area measure the total area of solid material. Therefore, it is hard to say that SAXS can replaced the surface area measurement (report).
SAXS data are trustworthy if they used in the way that they are intended. SAXS does not measure surface area but would derive it with bunch of assumptions. If you want SSA, use BET or an alternative technique which measures it directly.