I was confused by your terminology, thinking of the old chamber inserts which allowed, for instance, a .32-20 cartridge to be fired in a .30-'06 chamber. Now I realize that what is being sold is something altogether different, a cartridge case with reduced capacity to allow a .32-20 powder charge to be effectively fired in a .30-'06 chamber with no change in performance.
The only drawback I can see is the possible lack of longivity of the turned cases. I wonder how many repetitions of neck sizing they can endure before cracking.
I believe this is a variation on the idea of the "Everlasting" cartridge case used by Schuetzen shooters in the late 1800's
