My dad bought some of those last year and I did not find them to be very sharp. He had a new set that I thought he had shot through a Styrofoam target they were that dull. Also, the replacement cartridges are expensive compared to most replaceables because you are paying for the blades and the outer ferrule. ($20 compared to $9)I'd buy any of the following before the NAP Crossfire:

Fixed blades:
Slick Tricks
G5 Striker
Wack'em Triton or Exit
Wasp Hammer SST
Muzzy MX 3 or 4

Mechanical:
Rocky Mountain Snyper
Rage
Trophy Ridge Undertaker