How they really differ
Semrush answers "what should I target and who am I up against?" Frase answers "what should this page cover and how complete is my draft?" They overlap around content ideas, but Semrush goes much wider into technical and competitive data.
Semrush is one of the pricier tools in this directory and can be overkill for a brand-new site with a handful of pages. A narrower tool can be the better early purchase.
Using both
Teams doing serious SEO often use a research suite to pick targets and a content tool to brief and optimize each page.
The verdict
Brand-new site and writing-focused: start narrower, with Frase or even free tools. Search is a key channel and you need competitor and technical data: Semrush.
Want the full write-up on each? Read our Frase review and Semrush review.