It's a good thing there's an electric assist motor - tacking upwind, back and forth across a narrow street, would get tiring pretty quick. Not too mention very irritating to drivers of automobiles.

Hopefully, "more sail area" means they're adding a spinnaker option for the more adventurous people out there.

"...irritating to drivers of automobiles...."
You mean it would be a threat to their entitlement of the roads. Bring it on!
You'd have to be a pretty adroit sailor to stay out of trouble.
It would work for some people in some places

I tried this when I was about 12 years old, a few decades ago. I ended up slamming into the curb at such force and repeatedly, that I soon gave it up.
The notion of recharging the vehicle from "wind" is not clearly spelled out by the manufacturer. Since there is no wind turbine blades on the vheicle, one might conclude that the recharging from the wind is acheived by driving the vehicle at excessive speed, then "braking" the vehicle using the electric motor, down to the desired travel speed. To maintain the charging, the motor would be used to continuously brake the vehicle. Between trying to operate such a system, in conjunction with peering throught the plastic window on the sail, I would hope there is quite a legal document in place to remove the manufacturer from liability issues. Best of luck!

Plus cars would actually see you on one of those low to the ground trikes.

I can see it now...
Honest, officer, I didn't see the bicycle, it came out of nowhere.
You're saying you didn't see a three meter sail going down the street? You'll need to breathe in this, please...

I'm also wondering how stable this is...

Well, it's an interesting idea, but one that has been done a number of times. I'm not sure where they figure a person would use it most, but the safest bet would be on a hard packed beach somewhere. Bike paths, sidewalks, urban traffic - not a very practical solution. I can't imagine trying to ride it down the side of a road with windward being to starboard.

For the comment about a lack of clarity on implying the use of hte sail to charge the batteries, if a reader isn't smart enough to put the sail and the recharging together, they're also likely not smart enough to manage the system in the first place, so no loss there.

For the comment about it actually being able to be seen, there is no problem with visibility on a recumbent anyway. People run into trains, buildings, tractor trailors, bridges, etc. Doesn't matter how big or small something is, there will always be some (or many) morons out there that will not see it. From years of riding DF's and then switching to 'bents, I am much safer on a recumbent than an upright and have had far fewer close calls and drivers intentionally trying to sideswipe or run me off the road. The weird looking profile is enough to garner at least some curiosity and lots of motorists think they are some kind of wheelchair. That being said, it's also on the onus of the bent rider to be smart enough to ride as if they're invisible to a motorist and behave accordingly.