What benefits can a pen tablet or control surface provide in video editing?
I am a filmmaker/photographer; I have the shuttlepro 2 and a wacom intuos5 pro small...The shuttlepro2 is twice as much as the express but I have found it to be incredibly useful - more buttons = more customizable keystrokes. And the larger size is more ergonomic which will help with the transition and gaining the 'muscle memory' so that its the natural and fastest thing to do. Aside from needing to click shift, option, or command, I can edit (adobe pr/ae) without using the keyboard at all. This will increase your efficiency like crazy.

I do not find myself using the wacom tablet for video editing, although I did try it...The cool thing is that you can set up the radial menu with like 8 commands/keystrokes etc - being able to 'right click' on the pen and have all of your most common commands in a floating menu is awesome...however I found myself not really liking the pen for editing purposes. I have a kensington trackballpro - is had a scroll wheel and four bottons, making it excellent for use in a timeline, and its also really ergonomic.

I had the intuos5 pro medium and swapped it for the small - unless you are artist that plans on using this for sketching, you do not need that much real estate. You can map the tablet to the whole screen or map portions of the tablet for the entire screen; similar to a mouse, its most natural to have it set so that without having to move more than your wrist you can roughly reach all corners of screen, again youll only end up using a small amount of the tablet unless you plan on doing things like digital art, hand lettering etc.

The tablet really shines with photo editing. it has taken my work and workflow speed to the next level. Applying local adjustments in Lr or Ps is natural and much faster. And the ability to feather effects with the weight of your stroke can make edits more natural much faster.