I passed ACCA exams back in 96 so my experience may be a bit out of date. After long break from studying decided to take on taxation exams around 2003 and finished last year, passed each exam first time.
In my experience the taxation exams were not as difficulf as ACCA finals although they are not far off and the tax management paper at level 3 is on a par with ACCA finals (extremely useful however).
Two things to bear in mind:
1. I found the tax exams much more practical and interesting, some areas however such as trust law a bit boring though. If you are interested in a career in taxation you should certainly sit these exams.
2. The course content is very wide and considerable time is needed, however I worked through home study and the course materials are very good. I think the home study option is quite common among students.
If you invest the time and energy you will pass the exams ...good luck with it.