post-teaser does not tease (newbie)

I installed post-teaser 4.1.3 on WP 4.1 using theme twenty-forteen

I created a post and inserted the more tag (in visual editor) and confirmed to have the more tag <!–more–> where I wanted to in the textual editor.
However, when viewing the post, the tag seems to be completeley ignored.
Of course, that the plugin is activated.
In an attempt to investigate the problem, I changed a debug flag to true:
class post_teaser {
var $version = “4.1.2”;
var $debug = true;

But I have no idea, how $debug is used.
Any ideas, how to fix or further trace down the problems ?

https://wordpress.org/plugins/post-teaser/