I restarted the browser, downloaded a test file, and the download speed capped out my bandwidth exactly as expected. The "Registration" menu in IDM now shows a generic registered name, and the nag screens are completely gone.
: Usually involves a one-click "Patch" button that applies changes to the IDM installation directory. Security Risks and Malware Analysis idm 6xx patcher v21 top
IDM 6.xx Patcher v21 (often termed "top" in search contexts) is downloaded a test file