Appearing in Mock Interviews conducted by various coaching institutes is a decision that is solely yours.
It is proven fact that personality cannot be made overnight and if you are able to reach right people, you may be benefitted otherwise, it can be disastrous as you may turn out to be copy-cat.
What I have gathered from hundreds of toppers in last 25 years is that nothing helps better than group discussions with seniors/other candidates and your friend’s group as they are acquainted with you better than the coaching institutes people who know you for say few minutes or may be few hours.
For any successful interview, it is must that you have to be consistent with your views, opinions and you may need to support them with logic and facts. Your friends/group knows your strengths and weaknesses; they can help you form diverse views from various angles on a range of topics.
Clarity comes with arguments and your friends/group can grill you as they know where you lack and can be helpful in plugging the loop-hole if any in your preparation.
The experienced board members look for honesty, integrity and originality so don’t give them opportunity to spot that you are acting.