This garment is partially compatible with the breast slider. The strap running across the torso will not really stretch to fit different sizes of breasts, but it won't cause any noticeable clipping or layering problems if the breast size is changed. It can be used with various breast sizes.
Note: this costume is not compatible with the breast slider. It will set the girl's breasts to the correct size when the SWF file is loaded, but any subsequent size adjustment will cause the breasts to fall out or clip through the fabric.