I think it is safe to say that revising for any exam without the experience of practising exam papers would be a huge mistake.
These papers are essential not just for testing what you have learnt but also to see the style in which the examiners ask questions. I would strongly suggest anyone preparing for a grade 5 music theory exam to buy at least 2 papers and their model answers (sold separately) to get a 'feel' for what to expect and make sure you have covered all the different ways that they can ask the same thing. The advantage of taking these exams is that the questions are quite repetitive every exam period - for example there is always a question on intervals, composition, alto/tenor clef, transposition, orchestral instruments and with cadences at the end.
The only downfall with these is that they will only give you the answers and not the working or reasons. So, if you get the answers wrong you will either have to try and figure out why on your own or ask a teacher.
Remember that each paper you buy includes all the papers taken in that year, so from periods A,B,C and a specimen paper. So you are really getting 4 exam papers in 1. The model answers work the same way.
The papers are marked out of 100 pass = 66 Merit = 80 Disticntion = 90