Achievement Diary Capes are cut following the completion of every quest, making the modified version harder to obtain. Much like RS gold Quest Point Cape, this item gets cut back as a new quest is brought out. It only gets cut when all of the quests available in the game are completed. This means that every new mission has to be completed.
Both the untrimmed as well as the trimmed versions of this cape feature +9 bonus on all defensive stats , and a 4 bonus to Prayer skills, making it the best slot-untrimmed cape for Prayer. Achievement Diary Cape also has the ability to teleport daily to the Achievement Diary Master, which makes it a fantastic to transport items.
However, some of the achievements happen in Draynor Village, Varrock, Lumbridge and other free to play locations, Achievement Diaries are not available to non-member players. So even if you take the correct steps, it does not guarantee the cheap Runescape gold reward to the f2p player. While there have been numerous rumors about creating new Diaries only for players who are free, there is no evidence from Jagex.