Looks like a very useful machine. It seems awfully bulky, but then the CO2 tubes used in 150 watt lasers are probably around six feet long, so that kind of sets a minimum size for the machine. A 74 horsepower generator sounds like overkill, though.
I suppose they probably use galvanometers for aiming the laser? Galvos are very fast but they tend not to be terribly accurate. This device isn't for precision machining so it's probably good enough. I'd also expect the vibration and jostling of the machine to be a problem, but maybe it stops momentarily whenever it does a laser sweep.
I'd think that they really ought to have some kind of shroud draped around it during regular operation to prevent eye damage if someone is too close (especially if there's a risk of shiny metal objects lying on the ground). CO2 laser light is invisible; generally, you just see a white flash when it burns things because that's the light given off by the heated material.
There'd also be an obvious fire hazard, though in practice a well-focused high power beam can often just vaporize a thing before it catches on fire. Cutting paper and cardboard in a laser cutter is usually fine; it's wood that tends to burn. (Especially oily wood.) At any rate they'd probably be restricted to using the machine when fire risk is low.
I wonder how well it copes with weeds that are growing right next to desirable plants? As the crop plants get bigger, it must get harder to get the right angle to burn the weed without hitting the plant.
I also wonder how effective it is at actually killing weeds. Maybe if it can get them when they're small, it can linger the laser over the site of the weed long enough to cook the root.
I'm hoping this sort of thing catches on and becomes more advanced. Near where I live we have a huge park that's being overtaken by English ivy. It's very hilly and forested, so any ivy-killing robot would probably have to be something like a hexapod, and lasers are kind of questionable in a forest setting except maybe on wet days.