After thinking about this I realized one major problem with their approach (at least from a retro-fit perspective). In their case they are adding a valve between an existing plumbing fitting mounted in the ground and a commericial spray head. Even adding a straight coupling between the two would raise the spray head about 7/8" - to one inch. Adding a valve has to add even more than that. Now the spray heads only come in a fairly limited set of sizes so, without digging out the existing fitting or adding a swing joint, the spray head is bound to be a lot higher (or lower) than the original.
So, to your point, bumps in the lawn and potential damage by lawn mowers.
Of course, to Felix's point, you are saving the world.
But, niggling about the flaws in an unfinished product is not productive or worthy. I do really like the concept of individually controllable spray heads and, to your point, batteries, 'chemical' or otherwise, have a certainly predictability that I find useful in irrigation systems...
Tom