As a driver, I really like these timers. I can see from a block away that I've got 15 seconds (and will make it comfortably) or 2 seconds (and may as well slow down now since I won't be anywhere close).
As long as the blinders weren't too restrictive, my use case would still be viable.
The use case they caution about is drivers reacting suddenly to short clocks -- flooring it or slamming on the brakes -- when they're very close to each other. They're talking about how people react to a "2" when they're 2.1 seconds away from the intersection and right on somebody else's tail.
I'm talking about reacting from a long distance out by subtly adjusting speed (obviously in conjunction with reading traffic -- you don't accelerate if there's a vehicle right in front of you.) If you're 10 seconds out and see a 2, there's no differential reaction, likewise if you're 10 seconds out and see a 20. Even if you're 10 seconds out and see a 9, the difference between "slight acceleration" and "slight touch on the brakes" isn't significant unless you're already driving too close for the circumstances I drive under.
As long as the blinders weren't too restrictive, my use case would still be viable.