@ Aarthi

1) Bangar main book is what is required for preparation. The compiler will give you an idea of the kind of questions that come in exams. I am not sure whether the book is good enough for revision purpose because it just contains summarized points which at many places feel incomplete when you sit down and compare it to the main book. So to answer your question, it is necessary to purchase the compiler in so far as you feel you need extra practice of sums. If not, the main book is more than enough.

2) As to your second question, his book for DT is good and can be used for exams. However it's the kind of book that cannot be universally loved. Some may be comfortable with it; some may not be. Personally I started with Bangar but I have switched to Manoharan. Not due to any fault of the book but only because I am more comfortable studying from Manoharan. But I am still using Bangar for illustrations and some case laws. His book has 268 illustrations which come in very handy to understand certain concepts. Also some chapters I felt is better explained in Bangar than Manoharan so I will be using Bangar for those chapters. 

@ CMA Final

1) As to your first question, please refer my reply to Aarthi.

2) Secondly, can you please tell why Bangar compiler for DT cannot be relied upon? Many suggest that book for past exam questions and I mysefl intend to buy it. 

3) For costing I feel institute study material is pretty good. If you do need a reference book, I guess Tulsian should suffice. Personally I have not seen any text book for costing. I am doing the study material and practice manual and haven't had any problems thus far.

Bangar compiler for Dt is not good on a standalone basis. This subject cannot be studied like this in my view. Compiler is good but along with either Manoharan or Institute's material. But I hope there is a better book than Bangar compiler when it comes to illustrations as these are not enough to score good marks (once again through personal experience).

I will see how Tulsian is, as a reference book,

Thanks for valuable suggestions.