I have seen a large number of moving message displays with broken diodes. Maybe because of bad batches of diodes. Maybe because of not correctly controlling the current. Maybe because of hung software in multiplexed displays, feeding huge currents continuously into a single scanline. Maybe because mechanical abuse while soldering, resulting in micro-cracks letting moisture inside.

I have seen a large number of moving message displays where it hurts to look at the next at night because they don't have proper intensity regulation.

I have seen a large number of moving message displays where the intensity of the individual diodes varies a lot because of improper binning and/or current control.

I have seen a large number of moving message displays where the intensity of the individual diodes varies a lot because the diodes selected have very narrow viewing angle and the diodes hasn't been mounted with the required mechanical precision.

I have seen a large number of moving message displays where I have to take one step sideways or closer to see the text, because the viewing angle of the selected diodes are wrong. Some displays have managed to use asymmetric diodes but failed to distinguis between horisontal and vertial orientation.

I have seen displays where the intensity regulation is affected by the light from the display, resulting in a feedback loop.

The next thing is how to handle the blistering heat - the PSU and buffer chips may produce a significant amount of heat and with the sun feeding 1kW/m2 from the outside, it isn't so trivial to keep everything properly cooled.

It doesn't take much to crash and burn. And the rumours will spread the badwill to other customers.