It seems everyone and their mother takes cupped hand. Do people try and take the mirror shield or w/e its called?(The one that reflects a single magic missile spell back on a 2+) I haven't had the pleasure of using a Slann as I can only play in 1k games ATM, but I would imagine when sticking a Slann with a unit of temple guards, they get targeted a lot by magic missiles.
Can the Slann himself not take it? The unit will already have more than too many points in it without another hero, and the armor save on him would be more useful then having it on the champion.
Its not really worth it, magic missles are the least of your worries these days. Plenty of other spells around that do faaar more damage.