As a long time reader of the Wall Street Journal it was amusing to find this video on their website. Would we have seen this before Rupert Murdoch bought the paper? I doubt it for whatever that's worth.
I might have some confidence in this green gadget if the Journal's well respected personal technology columnist Walt Mossberg had reviewed it. I'm being felicitous. Not likely, unless Rupert ordered him to and even then, he'd likely have to hold a gun to Walt's head.
If you have no knowledge about plants and you have fifty bucks that you don't care about it may be worth it. Even then, I'm dubious.
One of the main features of this thing is its claimed ability to measure soil moisture. At this price, most likely it is a moisture meter measuring galvanic reaction to salts in the soil. Results with this type of meter are highly variable.
It is essentially measuring the soluble salts in the soil rather than the presence of water molecules. Put the meter into deionized water and it will read dry. High salts (fertilizer) in the soil can give a moist reading in dry soil. Caveat emptor!