The pros and cons of a mechanical drop away versus a string drop away.

Hello fellow bowhunters.I am about to buy a arrow drop away for my new martin onza 3.I am stuck on weather to get a mechanical drop away or a string activated one.What are the cons of a mechanical drop away if there are any at all?My cabales are free flowing already with no restrictions if i can avoid it id rather not get a cabek activated drop away.Please fill me in on some info?Are drop aways more accurate then whisker biscuits?