I have used e-readers for about a decade across four devices. The category has changed remarkably little, which is unusual in consumer technology and is mostly to its credit.
Why the display technology matters
The thing that distinguishes these from a tablet, and it is not a marketing distinction.
Electronic paper displays reflect ambient light rather than emitting it, like printed paper. There is no backlight behind the image, and modern devices light the surface from the edge rather than from behind.
The practical consequences are real. The display is readable in direct sunlight, where any emissive screen fails. It consumes power only when the image changes, which is why battery life is measured in weeks. And most people report less eye strain over long sessions, though the evidence on why is less settled than the marketing suggests.
The trade is slow refresh, limited contrast compared with a good screen, and colour implementations that remain noticeably muted.
What actually matters when choosing
Having used several, the list is short.
Front light quality, including whether it offers warm as well as cool light. Reading at night with a cool light is unpleasant and the adjustable versions are considerably better.
Physical page turn buttons, which sound trivial and matter enormously for one-handed reading. Devices without them require a screen tap, which is worse in every way.
Weight, since the device is held for hours.
Waterproofing, which is genuinely useful and not only for the obvious reasons.
And format support, which is the one that determines whether you own your library.
The format and ecosystem question
The thing that should influence the decision most and generally does not.
Devices tied to a single store, with content in a proprietary format protected by digital rights management, mean your library is a licence rather than a collection.
Books can be removed from a store, and there have been documented cases of purchased content being withdrawn from customers' devices.
Devices supporting open formats let you buy from multiple sources, borrow from libraries directly, and keep files that will still open in ten years.
Library borrowing in particular is a substantial and underused feature, supported by public library systems in many countries, and the ease of it varies enormously by device.
If I were choosing again, open format support would be the first criterion rather than an afterthought.
What has genuinely improved
Over the decade.
Resolution, from noticeably pixelated to indistinguishable from print at normal reading distance.
Front lighting, from absent to good, including warmth adjustment.
Waterproofing, which is now common.
And typography, which improved considerably once the devices had enough processing power to do proper hyphenation and justification.
What has not
Colour, which exists and remains muted and lower resolution than the monochrome equivalents. Adequate for book covers and diagrams, not comparable to a screen.
Refresh speed, which is inherent to the technology and makes anything interactive unpleasant.
Note-taking, which has improved and remains slower and less precise than paper on the devices I have used.
And price, which has not fallen the way most electronics do, partly because the display panels come from a very small number of suppliers.
The repair and longevity position
Worth noting because it is better than most categories.
These devices last. Mine have failed through battery degradation and one cracked screen, and the electronics have never been the limitation.
Battery replacement is possible on most models with moderate effort and available parts.
Software support duration varies and matters less than on a phone, since the device does one thing and an unsupported reader continues reading.
Which makes a used device a reasonable purchase in a way that a used phone frequently is not.
What I would tell somebody buying one
Prioritise open format support and library compatibility, because that determines what you can read and whether you keep it.
Insist on physical page turn buttons and adjustable warm lighting.
Ignore colour unless you specifically need it, since the monochrome devices are better at the thing they are for.
And buy the cheaper model, because the differences between tiers are mostly storage and light quality, and the reading experience is close to identical.
The library card
Worth its own note because it is the most underused feature in the category.
Public library systems in many countries lend digital books, free, through platforms that work directly on most readers.
Borrowing is a few taps once configured, waiting lists exist for popular titles, and the loan expires automatically.
For anybody who reads regularly this substantially changes the economics of the device, and a great many owners are unaware it is available.
Setup takes about ten minutes and requires a library card, which is free.
Format conversion
Practical for anybody with a mixed library.
Open source tools exist that convert between the common formats and manage a library, and they handle most conversions well.
What they cannot do is remove digital rights management, which is the actual barrier for purchased content and which is legally restricted in most jurisdictions.
Which is the practical argument for buying from sellers that offer unencumbered files where the option exists, since a file you can convert is a file you keep when you change devices.