The post-sizing is all I use the pistol FCD's for.
I still crimp with the seating die.
I could solve the same problem by sizing my bullets, and probably do a better job of it, but this is faster. Any cartridge that gets more than just a kiss from the sizing ring goes in the "blasting ammo" bag. I want to make sure my target ammo and my self-defense ammo chambers properly 100%.
So I kind of agree about "solution in search of a problem", and the FCD can screw up your ammo if you need oversize bullets or if the die is out of spec. But it still can be useful, and it's awfully inexpensive.