The new and improved cartridges for the 2nd Gen razors are not compatible with the 1st Gen handles. If you have any original Precision 5 or Smooth 6 razors, they will not work with the 2nd Gen handle. 1st Gen women's razors are also incompatible with the 2nd Gen women's handle.
The 2nd Gen cartridge only fits the new & improved 2nd Gen handle.
You can check out the 2nd Gen razors here: