I found Judy Diamond pretty expensive and dated for viewing public Form 5500 data, so I built this. You can view a plans 3-year (and counting) Form 5500 history with benchmark comparison for free. Gusto's plan as an example https://planprovider.pro/companies/gusto-zenpayroll-401k-plan
For $300 per year, you can download a competitor's client list, like Pension Assurance's 969 plans here - https://planprovider.pro/provider/pension-assurance-llp
Actively building out the tool, so let me know if there is a feature you would want.