“Most DMX (which is electrically EIA-485) transmitter chips are specified to give at least 1.5 volts across a 54 ohm termination, making a Zo (diff impedance, not resistance) of 50-75 totally fine, irrespective of the length of the run.”

Drivers will drive it OK that’s true. But the reflections from 75 ohms cable wired to 120 ohms terminator can be serious issue. If cable is 75 ohms, the terminator should be close to 75 ohms to keep the signal reflection monsters out.

3KV test of cheap disco light with circuit analysis.
https://www.youtube.com/watch?v=xyO4xq23zDs

This light was generously sent by Aramus for our edutainment. It’s a classic eBay/aliexpress/amazon special and actually usable for some applications, but does have the usual hazards associated with cheap imported products.
The unit is a very good demonstration of cost optimisation.

The electrical separation and testing of these products is not up to Euro-American standards. If using them with other DMX lights I’d strongly recommend isolating them on their own buffer to avoid the risk of damage to other lights in the event that mains voltage finds its way onto the DMX network.
As stand alone lights they have their uses. A single colour can be set by adjusting the RGB levels using the buttons on the back. To store each intensity setting you have to press “enter” before moving onto the next adjustment. If a colour is set and stored then the lights will automatically light in that colour at power up. The way they run the LEDs and the fact that they are all in series means that LED failure is almost guaranteed in regular use. But at the price they could be classed as disposable.
As with many of these lights that cram too much functionality into a small processor, they have their limitations. They often rely on the DMX controller putting out a full 512 channel frame to allow time to process their effects after grabbing their channels of data. If the DMX is not what they were expecting they can sometimes glitch or not work at all.
Many of the units are made by small manufacturers who buy components like cases and PCBs from other sources, so if you have 20 seemingly identical lights, some may have different software and behave differently.
It’s not uncommon for lights like these to crash and glitch their memory settings resulting in data being spewed onto the DMX network causing a data conflict and knocking out an entire section of lights.
The combined capacitive current leakage from a run of these lights could potentially give a strong shock from a network cable and affect operation of other lights.

This light did pass a 3kV isolation test, but the construction of the transformer with low voltage windings laid directly across mains voltage windings is an issue. Ideally the transformers would be wound with double insulated wire or have sleeves where wires cross and extra separation tape.