I'm suspicious of anything they have to advertise like that.
Though the ads are often pretty entertaining. If no one's tried it, maybe a trip to Mitsuwa (in San Jose) will turn up a knockoff product. I keep meaning to go over there for various things.
I've tried wheatgrass drinks a couple times, and ... yuck! But they weren't Japanese.
Randomly, I'm so sad they got rid of J-Pop TV on Sundays. boo.