Hi Jeremy,
They are significantly different. The following comparison explains it well: <a href="https://www.tek.com/en/documents/fact-sheet/3-series-mdo-spectrum-analyzer-vs-oscilloscope-fft-comparison">https://www.tek.com/en/documents/fact-sheet/3-series-mdo-spectrum-analyzer-vs-oscilloscope-fft-comparison</a>
Main points to take away:
- ~15 dB better dynamic range than scopeFFT
- Significantly higher bandwidth (Up to 3 GHZ)
These may, or may not, be important to you, depending on what measurements you are taking.