Is the book worth it to get? Or should I choose another book?
It depends on what you're interested in. If you want a sense of Alexandra's "voice" and her emotions and opinions, a book of letters like
A Lifelong Passion would likely be a better choice.
In general, Alexandra's diary entries are brief, abbreviated, and businesslike. There are notations regarding temperature, daily walks, the children's lessons, the family's health, religious services, and so forth. Reflection and introspection are rare. Some people find her style tedious and mundane, while others appreciate the small details relating to the IF's captivity.
Here's a sample of a typical entry:
Tobolsk 3/16 February
-11 Tuesday
Wrote & read.
1:00.
Lunched downstairs.
Looked through accounts with Zhilik.
5:00.
tea.
Rested. --
8:00.
Dined with Baby.
Spoke over money affairs with Valia.
Nicholas read to us.
Heard that dear old General Ivanov has been killed at Kiev & also Metropolitan Vladimir.
Syrobiarsky 18. [a notation regarding a letter Alexandra wrote]There are some annotations that explain and expand upon Alexandra's entries. These footnotes include short excerpts from Nicholas's diary, Gilliard's memoirs, and various letters. For me, it's been a valuable resource, but I think $50 is rather expensive.
Try
Bookfinder.com. I searched by ISBN (0300072120) via the advanced search pane and found copies starting as low as $10 (including US shipping).