I dont know about mazhar ul haq, but this I can certify to. Both Ameer Ali and PK Hitti are more scholarly and not exactly perfect for examination purposes. I myself studied these for a week or two and realized that I was making too little progress because I had to go an extra mile to extract the right information from the books, especially hitti. I'll try Mazhar ul Haq. From what I know and I've seen, it does seem like more "exam focused".