One of the local shop is selling 6061T6 lightweighted pulleys. Are these any good? What gains can I expect and will it harm the reliability of my 3.0L engine?

 

Does it have a harmonic balancer on it? If not, I would not use it.

The only brands I know of that carry pulleys with harmonic balancers are ATI and Boost Logic, at least for the supra guys. But it might (and probably will) fit the GS300. Someone correct me if I'm wrong.