Will a SMARTpool reagent result in more off-target effects since it involves adding four different siRNA duplexes at once?

It is unlikely that a SMARTpool will have an enhanced off-target effect. Each siRNA has a unique off-target signature, which can be identified by microarray analysis. When the siRNA is present as a fraction of the total concentration as with a SMARTpool reagent, Dharmacon scientists have found that the off-target effects from any one siRNA are minimized and reduced. Any sequence-independent effects of the siRNAs will either be the same as with a single duplex or reduced.