What is the difference? I keep hearing people say that if you have all the same 4 servo then you should be fine, while some say the three cylic servo should be different from the tail? I am confused.

I am planning to buy all 4 of these exi servo. Three for the head and one for the tail. Will i be okay?

http://www.xheli.com/exi-servo-d213f.html


Thanks!