Avinashh, you are absolutley right! But the services idp provides at the test center must be appreciated. They are really professionals compared with BC. I experienced it since I have tried both of them.
In my opinion, test centre doesn't make any difference. If you stay calm and focussed, you can get it. I have tried both and the only difference I could see was the hospitality which was better in IDP. All the best !!!