I gave 2 tests, 1 with British Council and 1 with IDP. I felt IDP was simpler as far as the question and the exam content were concerned, but that may be because I had better practice the second time, I use to practice a full test everyday for 2 weeks before my second test. I scored overall 7.5 (L 9, R 6.5, W 7, S 7.5) with BC and an overall 8 (L 9, R 8.5, W 7, S 8) with IDP. I think practice and confidence is what you need, doesn't matter if its IDP or BC. However, from earlier posts, many people think IDP is simpler so give it a shot with IDP.