You can tell from the doorway which desks have a monitor arm and which ones have a monitor just sitting on a stack of old textbooks. One looks like someone thought about where their neck would be in five years. The other looks like a temporary fix that's been temporary for two years running, screen tilted back, cables dragging across the keyboard, the whole setup inching closer to the edge of the desk every week.
If you're starting from nothing, go with a single clamp mounted arm for one monitor before you even think about a dual arm or a screen with a built in stand. A basic single arm will hold most monitors up to around 27 inches, clears your desk space by lifting the screen entirely off the surface, and gives you the up, down, forward, back and tilt adjustment that a fixed stand never will. You want the screen's top edge roughly at eye level, which for most people sitting in a normal desk chair means the arm sits around 12 to 16 inches above the desk once it's adjusted. Get that right and you stop angling your whole neck down to read email.
Where this goes wrong is desks that are too thin or too flimsy for a clamp, anything under about three quarters of an inch thick, or glass desks without a reinforced edge. The clamp needs something to bite into, and a wobbly desk will transmit every bump of the arm straight into the screen. It also doesn't belong on a desk you share with a laptop stand and a second small screen crammed into six inches of space, because the arm's reach needs room to swing without colliding with whatever else is parked there.
The honest limit is that an arm does nothing for you if your real problem is desk depth, not height. If your desk is 20 inches deep, a monitor arm just moves the screen around in the same cramped footprint, it won't give you back room you don't have. And if you're using a laptop as your main screen rather than a second monitor, most arms aren't built to hold it well unless you buy a specific laptop tray attachment, which is its own extra cost and another thing to adjust.
For finish, matte black or white arms disappear against most desks faster than silver does, and they hide fingerprints and dust better too. A white screen panel reads calmer in a small room than a dark one, since it reflects less and doesn't loom the way a big black rectangle can in a tight space.