Anyone used internal linking automation plugin?

Has anyone here used Internal Link Juicer or a similar internal linking plugin?

I have 2 questions before I take the plunge

1. Do these plugins add the internal links to the post content or are these inserted on the why when the page is served by the browser, like in real-time? The latter may impact speed.
   Maybe this is a stupid question, still asking
2. Has anyone seen a positive impact on SERP after using these plugins?

Appreciate your candid feedback.

Thanks