… doesn’t have to take that much care of usability. And the installation routine of EditPlus certainly doesn’t.

Besides the fact that this dialog appears when it’s already too late (after the installation has completed) and that it contains redundancy (the “Send To” entry and the additional context menu entry do practically the same), the marked wording is very ridiculous or can you imagine a mouse button with an attached (?) editor?
As usability would not matter (remember: programmer’s editor) that much, a more useful and less ridiculous wording would be “Add EditPlus to the Context Menu of Explorer”.
The wording is one of the things that are very often very wrong in software by semi-professional companies (not excluding my own software) and this usually gets even worse in the installers as they are often not very well tested (or not at all). Those InstallShield things are the worst as many developers just click together the installation, then click through the dialogs and put the thing on the web.
This is the reason why my parents still have not succeeded in installing software on their own while nearly everything else went quite well the last year.