• Changing the speed of Rigid Bodies will distort the way they bounce. This is a Blender limitation. Rigid body sims without lots of self-collision (stuff like explosions and fractures) work just fine, as long as there is no bouncing involved. If you do need to slow down a bouncy rigid body sim, the easiest workaround is to bake the visual transform of the rigid body (Object > Animation > Bake Action) and then add the resulting action to the action box of the addon.
• Videos and other images that are animated within the 'Image Texture' node aren't affected by the addon. Sadly there's no way to affect the frame progression. Even if there were, slowing the scene down would produce choppy video playback since Blender doesn't provide any frame interpolation algorithms for video.
• Animations affected by Scene Speed behave weirdly when you use the right or left keyboard arrows on the timeline. This addon uses Blender's 'Animate strip time' function for NLA tracks. Sadly, when you use the left or right keyboard arrows to move the playhead on the timeline, the animation preview gets offset by 1 frame. Directly clicking on the timeline instead will show the proper animation position at the desired frame.
• Isn't compatible with the "Lock Interface" option in Cycles. This one's on Blender once again. Easy Slow-Mo relies on keyframing the strip time of NLA tracks. As of Blender 4.1, when "Lock interface" is enabled, it will only render the first frame of any NLA strip that has its time keyframed. Thanks to ss_kuroz for figuring it out.
  

Here's what you do if you initialized an older version of the addon in your project:

1. If you haven't already, uninstall the previous version, restart Blender (Important) and install the version 1.28
2. Create a new scene in your project, click on 'Initialize' and you're set! (make sure to not delete this scene you created)

Simply select the armature or object you want to be affected by the addon. switch over to the Dope Sheet tab, there select the Action Editor menu; The action name will be there.

Sadly keyframing a Camera's Field of View doesn't produce an action. The simplest workaround is to create an empty; then, add a driver on Camera's Field of View that would depend on the empty's X scale. This will allow you to use the empty to control camera's FOV; attributes like X scale do produce actions.