i never got any troubles using that spell
i usully use 1 griffin(for unlimited relation)
or when i get a demon
they are usually low stacked
so in any case i got one anyway
i move them up close
and let them fight ^^
while my ranged take the heavy units
u just have to be more carefull
in the swamp use this on a bridge

where only 1 stack can move through at a time then this spell is PERFECT
but then again it's only really usefull if u don' t have resu/gift/sacri