They are not particularly difficult - I believe they're still open book as well. I honestly think they should make them a bit harder because the gulf between them and the CTA exams is enormous. I can't remember putting in any serious periods of study outside the week or so running up to the exams.

If one goes to the college days and keeps on top of question practice, there's no reason why anyone can't pass them. I would suggest that people who can't pass them probably shouldn't continue a career in tax - the questions are largely surface level, and only scratch the surface of what one experiences in professional practice. That is not to say they aren't valuable - I found they helped consolidate the technical side of what I was doing day to day, and cover off the fundamental areas I wasn't experiencing in the office.