[Taskmage]

I was just soloing things for 140 exp, but the point is that the bonus you get is proportional to the experience you would get normally. So if you soloed a decent challenge mob that gave 50 exp, you would get 87 exp instead, because 75% of 50 is 37.5 and 50 + 37.5 = 87.5

Generally people use those bands in exp parties because it's easier to get the most exp from them that way.