I don't see the point, there could never be enough to link them together. Even if everyone on earth had one. It would need to connect to something besides peers, like smart phones do. We already have those.. If they were all in range of each other, how could they communicate with the block chain? Even if it worked as promised. I would be impressed if one person in every 500 miles bought one. Let alone 300 meters.
I'd buy one today.
And yes, they could work well, in theory. And yes, they would need routers in addition to peers, but those would be provided by retailers. The mesh mechanism is to extend the functional range of such a device, but is inmaterial for a bitcoin device. A disconnected bitcoin wallet isn't disconnected when you're home, only while you're out using it. So it can update it's blockchain (assuming it needs it, but it shouldn't) while you are at home or otherwise within wifi range of an open hotspot. The devices need to be able to broadcast transactions, & hear other transactions, to protect the owner from a possible form of theft by deception. Namely, if the device didn't broadcast transactions until it could connect to a wifi hotspot, a criminal could pretend to buy the car you were selling on Craigslist, pay you with bitcoin using both your wallet devices, and after you drive away the thug you paid to mug him would destroy his wallet device. Thus giving the fraudster the chance to overwrite the transaction that he paid with on his own device and keep the funds. If all bitcoin devices broadcast all transactions immediately, the fraudster in this scenario can't know if the transaction was heard by another wallet device, another person's cell phone, a router connected to the internet or nothing at all. This lack of certainty removes the potential gain from such a criminal strategy. It's not really speed of transaction propagation that is critical, but the
potential of same. If bitcoin is ever as popular as Paypal, we can expect that retailers that start accepting bitcoin are going to also invest in a receiver for broadcasted bitcoin transactions, since it's in their own interests to make certain that transactions make it to the Internet as quickly as possible to prevent double spends attacks against themselves. Although it would be possible to exclude transactions that don't concern the retailer, the additional overhead involved in making such a discriminating router would most often exceed the marginal additional cost of simply forwarding every bitcoin transaction that it hears. A store the size of WalMart could get away with only one such receiver per store. A mall might need two or three for all the stores, depending upon it's size and layout. A bunch of small stores down main street could get together to sponsor one for the whole block, although the costs of such a receiver if you already have Internet access at the store (who doesn't in America anymore?).
Theories aside, there wouldn't need to be a critical mass for such a device to be useful, and in places with retail density, the mesh traffic might actually be counterproductive. It's when you're far from a retail outlet doing business that such distribution of the transactions are necessary.
