I once thought about the same thing. The advantage over FLS that I can think of:
1. Saving the $ to buy FLS die, esp. if you already have neck sizer.
2. Theoretically enhance accuracy of 223 rounds.
3. Saving some time and hassle to do FLS
4. Lower the consumption of FLS lubricant
5. easier to adjust shoulder height and neck outer diameter
6. Help to improve the longevity of the 223 brass
7. Looks cool and maverick