I got some of the JSB .25 Knockouts and tested in three of my guns. My Georgia Airguns tuned Cricket was the only gun that shot them as well (BUT not better) than JSB Kings out to 75 yards. That said, I'm sure there are many others that have shot ammo such as the NSA's with much greater success.
I've just not been able to get on the slug bandwagon. For me..... the additional cost of slugs does not out weight the performance of the two ammo's at this time.