This calendar is a great way to remind yourself to pray for the nations.
The Operation World Book is bigger and has more information on each country but doesn't sit nicely on your desktop or dining room table etc. The calendar information is pretty up to date - last edited in 2002. It seems very current.
The info on each flip page is organized well and gives you essential facts and suggestions for informed significant prayer. It gives you 2 or 3 days to pray for each country, in case you get too busy or want to pray for other things you won't get behind or feel "under the pile" with this calendar prayer aid.
The calendar is not linked to any specific year. I.e, January 1 is not necesarily "Monday" or something, so you can't use it to figure out what day of the week it is, but instead it is designed to be used any year, year after year, praying for specific countries throughout the year as you flip the pages every couple days. The pages do have dates on them like "January 1-3", "January 4-5", etc.
Quality made and look. I am a current missionary and can vouch for the accuracy of the details.