[timdierks]

You should seek out a flare if you can, it's much much brighter than seeing a satellite or the ISS, as impressive as those are.

[Bromskloss]

Hmm, so an Iridium satellite is much brighter than a satellite or the ISS (a satellite). Got it!

[Stratoscope]

An Iridium flare can be much brighter than any other satellite including the ISS.

The Iridium satellites are not very bright most of the time - you would be lucky to see one with the naked eye. But when they flare, they can be the brightest thing in the night sky for a few seconds.