I tested them last year and was not impressed. The are supposed to have been improved, but you still can' t change the bleeders or main blades and they didn' t prove very strong in my tests. On the other hand the Magnus stinger 4 blade 100 grn was very strong, sharp and accurate. You can also sharpen or replace both the main and bleeders blades when needed. I think the Magnus head is just a much better product overall.