ElementsKit is an Elementor Add-on Pack. Elementor is a popular WordPress page builder with over 5 million active installations, and ElementsKit adds additional functionality to Elementor’s core widgets.
Elementor Add-ons are not new, in fact, there are dozens of them on the market. I recommend limiting the number of add-ons to the absolute minimum and only choosing add-ons from reliable developers. The reason is, each add-on plugin causes potential security and compatibility issues for your site as Elementor itself sees updates. The developer of the add-on pack needs to stay current or your site could stop functioning.
ElementsKit is not currently one of the top creators of Elementor add-ons, but they are not brand new either. They currently have 200K active installations of their free plugin on the WordPress repository. Prior to the AppSumo offering, ElementsKit used ThemeForest as its primary sales platform.
ElementsKit does offer something extremely interesting, and that is a feature they Widget Builder that lets you take code and create your own Elementor widgets. This appears to be a nice bridge for someone who knows a little code but is not comfortable creating a widget without some assistance.
Check out the demo of Widget Builder:
ElementsKit is available at AppSumo for a one time payment of $49 for 5 sites, stacking up to 3 codes unlocked unlimited sites.