Ah that's fantastic; finally a solution to the age-old problem of... erm, oh, hang on... QUICK - someome find a water-tight, provable justification for it - QUICK! 
They can be updated automatically from a central database. You can change prices in real time. Just like Amazon does.
And when all this "smart" junk goes wrong, then what? A shelf-stacker could remove a paper slip and replace it in around 2-5 seconds, and no servers needed. Yet another example of making a simple, age-old system over complicated "just because"; just because you CAN do something, doesn't make the fact that you saw it through to execution, "better".
Power cut = no e-ink update = problems. People are stupid.
I'm not normally one to support "smart" technologies (especially crap you see stuffed in people's homes these days) but e-ink tags is one example of a great use of a solid and well understood technology.
There is very little to go wrong and if the tag is faulty, simply remove and provision another one. If there is an issue with the infrastructure, the tag is stuck displaying the previous price. No big deal. I can guarantee large supermarkets have some pretty tight SLAs in place when it comes to their IT and core infrastructure.
The 2-5 seconds spent replacing shelf tags, applying special pricing etc... is such a wasteful use of staff (then there is all the back-of-house maintenance such as updating databases). Multiply those few seconds by hundreds or thousands of items in a single store that need updating and straight away that time adds up. I would rather staff focus on things like keeping shelves stocked, customer service and store cleanliness than spending days changing paper tags.
Amazon, Microsoft and Google all use e-ink displays on their "sneaker-net" data transfer solutions like the AWS Snowball. Why? Because it works!
Even small local supermarkets have back-end servers and databases powering their point of sales systems. If anything was to fail, it would be due to the lack of redundancy and backups. When you go to your local store and a barcode is scanned, there are networks and systems in place right there. I honestly can't remember the last time someone manually keyed in the price of an item. An e-ink shelf tag failing is the least of their concerns (and one which is quickly, easily and cheaply resolved).