How much weight can it hold in total?

The arm is rated for 44 lb across both monitors, so roughly 22 lb per screen. Check each monitor's weight with its stand removed before buying.

Does it fit curved or ultrawide monitors?

It can, as long as the monitor is within the weight rating and has a VESA 75x75 or 100x100 mounting pattern. Very wide screens put more leverage on the arm, so stay well under the limit.

Can each arm move independently?

Yes. Each arm has its own gas spring, so you can set different heights, angles and portrait or landscape orientation for each screen.

How does it attach to the desk?

It uses a desk clamp or a grommet mount. The desk edge needs to be thick and solid enough to take the clamp without flexing.

Does it include the VESA plates and hardware?

Yes, VESA mounting plates and mounting hardware are part of the kit. You supply the monitors and their VESA compatibility.

Is it better than a single heavy-duty arm?

It saves one base and clamp on the desk and keeps both screens aligned. A single arm per screen gives more placement freedom if your monitors are far apart.