Atomoxetine doesn't really lower norepinephrine, it's a reuptake inhibitor and as such it will increase the NE effects.
Clonidine works by agonizing NE auto receptors and effectively reduces the amount of released norepinephrine. A good anxiolytic and non-addictive sleep aid.
Lets not forget that the metabolite of strattera is a kappa agonist which could produce undeseriable effects, unrelated to its effects on NE.