HI MATE
The inserts in the bizerk barrel are made from stainless steel and are supposed to be very tough and hard wearing. The freak inserts are made from aluminium and are more prone to damage.
I have heard stories of the freak inserts being bent quite easily. Whether this is true or not I do not know. Personally I think there are better insert systems than the freak. It was the first (i think) but has now been taken over. The bizerk and the multiple switch system are good examples. Plus they are cheaper.