I have not taken it myself but they should be close to the level of difficulty that would be expected from the real thing. For practice however you might want to consider taking exams that are harder than the real exam
I have taken this test and also have tried other mock exams and in my own opinion, mock exams are harder. I guess the free sun proficiency test was just the tip of the ice berg. you'll encounter much more harder tests which will make you tougher for the actual exam and is exactly the point of the exam study guide authors.