If they can customize the shape of the cup, and whether it fits closer or further apart, I'd say it's a good idea. Otherwise, it's probably only helpful for those who don't get the concept of proper cup size and/or those who size up their bands 5 inches.
for instance, I can take any number of bras that don't quite fit me and hold up one cup on one boob and it will encase that boob. But, put it all together on a bra and it's no good. Underwires don't start and/or end in the right places. Straps are too far apart, near the armpit, etc etc etc