if the primary concern of adding plugins is related to performance, then you have nothing to be concerned about with GenerateBlocks.
The only code that GenerateBlocks adds to your site is the necessary HTML and CSS required to display the content you build with it. So:
If you had a page with no GenerateBlocks blocks on it, GB doesn’t create any additional code.
If you added 1 GB block, it only adds the code for that 1 block.
If you added multiple blocks, it will output the code for just those blocks and consolidate any duplicate CSS those blocks may share.
With Wordsmith the GB plugin is primarily used on the home page and static pages for the hero section and some other content. To put it into perspective the CSS that has to be downloaded for GenerateBlocks on the home page is a compressed 1.3kb. The stylesheet that WordPress core loads is a compressed 11kb.