It's a toy. And it's more than my opinion. Professionals use professional equipment that can properly measure to ensure stations are kept within government standards. Using toys like consumer grade SDR's are fun and educational for amateurs and hobbyists, but someone using them as a measuring tool for deviation, spectral, or occupied bandwidth compliance without being able to confirm it with proper test equipment and methodology, are being foolish. The Nautel tools are expensive for a reason.
Was doing a similar comparison just the other day: One of my colleagues claimed that WinTV SDR used in combination with a $300 test software running on a laptop would equal the measuring capabilities of a $35,000 Trivini Streamscope for DTV measurements. Side by side, the Streamscope blew the SDR out of the water. Not just with accuracy, but with granularity and level of precision.
If you've been in this business as long as I have, you would know that already. This is a discussion board. You can disagree and get defensive about the capabilities of SDR's, but it doesn't mean I'm wrong.