How much improvement in SEO can I expect?
With Plug in SEO Plus, you'll be able to improve your overall search engine visibility so that you appear for more keywords and more frequently. The 'search engine impressions' and 'indexed pages' are the two metrics in Google Search Console (Webmaster Tools) to keep an eye on.
Nothing with SEO is guaranteed, so trying things out and measuring is important. We've written a bit about this here:
As you use Plug in SEO Plus, working through the walkthrough videos and making it a part of your day-to-day shop activities, your search engine visibility should gradually increase over time.