An e-book is much like any other book, except that it is delivered as a file rather than on paper. For craft they have some real advantages, and a few drawbacks worth knowing.
The advantages
Immediate. You buy it and you have it. No waiting, which matters when you want to start something now.
Searchable. Finding a specific technique in a large reference is far quicker than flicking through pages.
Printable in parts. Print only the pattern you are working on, take it to the sofa, mark it up, and reprint if it gets covered in tea.
Zoomable. Genuinely useful for charts and small photographs, and increasingly relevant as eyes age.
No storage. A shelf of craft books takes real space.
Cheaper, usually, with no printing or shipping cost.
Independent authors can publish. This is the significant one. A great deal of the best current craft material comes from individual designers who would never have got a print deal, and e-books are what made that possible.
The drawbacks
A screen beside your work is less pleasant than a book, and more fragile around yarn, scissors and tea.
No secondhand market, and you cannot lend it or pass it on.
You may lose access if a platform closes. Download and keep your own copy where the licence allows.
Harder to browse. Discovering something you were not looking for is what a physical book does well.
Judging one before buying
Look for a preview. Most sellers offer sample pages. Look at the photographs and at whether the instructions are written clearly.
Check the format. A PDF laid out for print is far more useful than a reflowable format for anything with charts, because the layout stays put.
Check what it covers, specifically. Vague descriptions frequently indicate thin content.
Read reviews for mentions of errors. Self-published craft material is not always technically edited, and an untested pattern is worse than no pattern.
What makes any craft book good
The same things in digital or print. Clear photographs in smooth light yarn. Stated gauge, yarn weight, hook or needle size and finished measurements. Instructions that have been tested.
If a pattern collection omits gauge and finished measurements, the format is not the problem.
