If you are truely doing a freq response then you need a calibrated mic or SPL meter. If all you are doing is level setting or looking for rough peaks/nulls at base freqs then you will likely be ok. The advantage of the RS unit is that there is a calibration file (not specific to the unit but specific to at least the model #) for the RS unit. Again for base freqs this is likely good enough. But at higher freq's the RS unit is not all that acurate either and you are back to needing a calibarted more expensive unit if you want accurate measurements.