The should include a camera in the device as well - just to record reactions when people take it out of their bag at airport security checks.
The only way I can see they could have made it look more threatening would be to write "Atomic Bomb" in large letters down the side and have a large LED display counting down to zero in 15 seconds or so.
290Wh is not allowed no board aircraft as per ICAO rules Annex 18, the maximum without a specific agreement from the airline is 100Wh. With the agreement it's 160Wh. "Lithium batteries exceeding 160Wh are prohibited in both carry-on and checked baggage."
It seems you're right. It is allowed by FAA but disallowed by ICAO. I'm not sure I would take any chances with a 300$ device though
Passengers can also bring two (2) larger lithium-ion batteries (more than 8 less than 25 grams of equivalent lithium content per
battery or about 100-300 watt hours per battery) in their carry-on.
The only way I can see they could have made it look more threatening would be to write "Atomic Bomb" in large letters down the side and have a large LED display counting down to zero in 15 seconds or so.
Edit: The perfect add-on for your reactor: http://www.instructables.com/id/Crazy-Countdown-Timer/