Yes — SEO Booster works great with your existing SEO plugin. SEO Booster is not a replacement. It’s a new tool!
There is nothing that Yoast SEO plugin does, that SEO Booster does. They work well together though.
Both plugins handle SEO related matters for WordPress websites and I use the free Yoast SEO plugin almost everywhere. I have several Premium licenses for myself and clients as well.
In fact, I recommend you install and use Yoast SEO and use the Focus keyword feature in particular.
Not only do you get to use the many features in Yoast SEO but keywords can automatically link to your pages.
This way, if you optimized one of your pages for «butterfly cookies» — Turning on the right option makes every occurrence of the word «butterfly cookies» turn into a link to => mysite.com/butterfly-cookies/ — all by itself. Neat, right? 🙂