honestly, i can't realy tell, because in my approach i use the same key for master and slave, so its normaly something accessible like 1-9 and so on...
..but if i would use hidden keys, they would be mostly keys on the right side of my keyboard, as i don't use them for normal gameplay (like i,o,p,j,k,l,n,m...).
As Typing is concerned: When i have to chat i normaly (if i don't forget) stop keyclone from broadcasting, if i want to type a command to all my toons I also use the corresponding function in keyclone, so there would not be an issiue, i think.