Elementor vs. Guttenberg? Is it going to affect my SEO?

Hey guys, I am switching my site from a Duda to WordPress and I want to make sure I'm not setting myself up for endless expenses down the road. I'm fairly experienced with Elementor and I decided to use a vendor for the migration to WP. The vendor is recommending that I use Guttenberg rather than Elementor. They're recommending that they build the theme template pages in Guttenberg using their code and then all I'll have to do input the content and pick the page template. They're telling me that Guttenberg will increase the speed and will help with SEO.

Am I setting myself up to be tied to them forever when if I go with Guttenberg? They're also pitching a maintenance package and switching my hosting.