I'm out of date. Does E-ink still have ~500ms latency of refreshing the screen? If so, that's the #1 reason I believed it wouldn't be successful when I used them 6 years ago.
I was blown away when I was able to write some technical specifications in emacs, render them to PDF and share them to the device, then go for a coffee and review my work. I can markup my documents, sync them back to my machine, etc.
I do wish the resolutions of the documents on my desktop were better. I've drafted presentations on the device while thinking. I vastly prefer paper for thinking. This device is perfect for that.
I just wish I could do more with it. I want to be able to hook up a cloud service to interpret my math hand-writing, run it on my theorem prover or checker, and return the results, etc.... much like what people were doing in Xerox Parc ages ago.
Do you think it would work well for someone who sketches for a living? My wife is a fashion designer and her minimum setup of a MacBook Pro + Wacom is pretty unminimum.
[edit: Reviews I read said that the drawings are scalable vectors, but two posts below talk about poor resolution, so maybe not the right device for her]
I'd consider the latest iPad Pro better for sketching, thanks to high frame rate and no lag, pressure sensitivity control, pencil "angle" control, and iPad-native software options have BnL surpassed desktop.
// Digital ink junkie since the Newton, currently own and use latest models of Wacom Cintiq, Surface, iPad, and Remarkable.
I have a few artist friends who are pleased with the Microsoft Surface. You get a pressure-sensitive stylus like on the Wacom and can run full versions of Photoshop or whatever.
It's not for everyone, but it might be an option for your wife to consider.
I have one too. The drawing/writing is pretty great, though once it's transferred back to a PC, the resolution seems kind of poor. Not too bad, but I'd like it to be smoother.
The only other major issue is software stability especially when reading. I've had it hardlock while reading something, then have to wait for the battery to drain because it won't respond to any input, then once I have it back up it forgot where I left off so I lost progress. So for the time being it sits, though once a software update or 2 come out I'll try again.
I would argue that e-readers actually do need reasonably low latencies. The reason I still read books is because I can flip through pages quickly and glance over 20 pages a second as I look for the page with a certain pattern of text or an image.
Not sure how specific you're trying to be - here's a specific example of 4.2" at $35. I actually would be interested to see a graph of cost-per-square-inch to see where the arms and legs actually do come into play.