The shelf top is made of the same high quality material as the graphite workstation top. The supports are extremely strong and made out of thick flat tube steel and rated at 100 lbs by Raxxess (this is one time I take their word for it). Can easily hold any size active monitor without bowing. These shelves are not height adjustable but there is at least 5" of clearance, which is enough to slide most control surfaces under such as MIDI controllers.
I recommended purchasing two of these to elevate your monitors off the desk surface.