Suggestion for moving $readmore

In tooltip_html you append the $readmore string to the excerpt. This has the effect of adding “more” to every excerpt regardless of length. Have you considered moving it to get_the_excerpt? E.g.
if ( strlen( $excerpt ) >= absint( $this->settings[ 'excerpt_limit' ] ) ) { return substr( $excerpt, 0, absint( $this->settings[ 'excerpt_limit' ] ) ) . '...' . ' <a href="' . get_the_permalink() . '">' . __( 'More' ) . '</a>';}

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