I passed using primarily the Life in the UK test prep app by The Stationery Office. I was feeling rather confident when I was consistently getting 100% on all my practice/mock tests. But then I randomly decided to look at one of the free sites online and did rather poorly on the first practice test I took, so I started reading the text material (which is available to read on at least one of these free sites)...
On the day of the test, there were a couple of questions in my random selection that I wouldn't have known if I hadn't done that extra bit of reading. I still would have passed the test, but I would've been a bit more unsure of my result.
As it was, the information that was quizzed was the same, but the structure of the questions was slightly different between my app and the actual test, so a couple of questions gave me pause. I flagged those and revisited them after going through the whole test. I was happy to have 21 that I was absolutely sure of, and then 3 more that I was iffy on. I would've been iffy on 5 or 6 if I hadn't done that extra reading, and you can only miss 6 and still pass.