When I was giving grinds I used both the "Less Stress" books and O.D Morris, Text and Tests. I found the "Less Stress" books were great for revision but if I ever needed a detailed explanation I'd just ask O.D.
I'd recommend Roantree and plenty of past paper questions. I failed my 5th year HL Maths summer exam (20%)..Had to teach myself the full course in 6th year and got a B in HL in the leaving. I put it down to doing EVERY past question at least 5 times : ) Hard work but it paid dividends!