It's an ambidexterous magazine release lever, developed by former senior FN engineer Leon Hubert and sold by BH Spring Solutions. It's easily installed, and operates as a lever system. In actual use, it's totally unobtrusive. While I rarely use it to eject a magazine, I look at it as a "tool in the toolbox" sort of thing; it's a situationally cionvenient option. It uses a slightly lighter than OEM magazine catch release spring, but not so light to cause any inadvertant magazine releases. It's sold as a set (the magazine release, spring, and ambi lever), and the lever pedal itself can be detached from the component. They have a similar set-up for the High Power and Glock; I have one on my High Power (which for some reason I find myself more likely to use than the one for the 1911, but am not a fan of replacing OEM Glock polymer parts with after-market metal ones, so it's unlikely I'll ever request one from BH Spring Solutions to test.
https://bhspringsolutions.com/index....s-mag-release/
Best, Jon