These are experimental features and good to try them out on the sandbox site. But otherwise and by all means, I would avoid them on a live website.
Do I have to use the Gutenberg plugin to get access to these features?
It depends on the feature you want to use! Keep in mind that each version of WordPress after 5.0 comes with bundled versions of the Gutenberg plugin, automatically containing new features and changes. If you want the cutting edge features, including more experimental items, you will need to use the plugin. You can read more here about whether using the plugin is right for you.
Besides, the level of customizations, features & options that GenerateBlocks would offer can’t be expected in the default Gutenberg blocks.