Can you actually run on the Merach T12?

Only slowly. Top speed is 5.5 mph, which is a brisk jog for most people. It is built around walking and light jogging, not running training.

Does it work under a standing desk?

Yes. With the handrail folded down the deck sits flat, so you can walk while you work. Check your desk height and the deck's folded height before buying.

How much weight can it hold?

The maximum user weight is 300 lb. The 3.0 hp motor is sized to keep the belt moving smoothly near that limit at walking pace.

What programs does it include?

It has 8 preset programs that vary speed over a session. You can also set speed manually from the handrail controls.

Is it hard to assemble or move?

Assembly is mostly unfolding and attaching the handrail, and it rolls on transport wheels when folded. It is heavy, so moving it upstairs takes two people.