When I got to the very end, the last window (install success) was dead. Clicking anywhere on it just produced a ding! I couldn't tell if there was anything under it, but an elevated TCC (v18 build 14, in fact) said the only windows belonging to the install TCMD were the components of the window I was looking at.
h:\work> whichwin /p 2336 /r /v /f t Take Command 18.0 Setup Run Take Command 18.0 View Readme File &Close Take Command 18.0 has been successfully installed. Line Icon Bitmap