We certainly don’t recommend using 2 primary keywords for 1 page.
Ideally, 2 primary keywords should have 2 different pages.
If you properly optimize a page for a primary keyword, you will also rank for secondary/related phrases or keywords.
Strell provides you with the relevant secondary keywords to add to the content in keywords section.
It also gives you clear direction about what to use in headings, titles, and content.
If you follow Strell’s recommendations, you’ll see better rank for more keywords over time.