Well... they are 15mm x 15mm x 15mm and are tuned to the wavelengths better than the cube in the sleds. Also, the larger size means they will hold the beam rather than have the edges spraying out of the sides... and they are meant to be used for combining beams of the same color, while the ones in the sleds (not sure, please correct me if I'm wrong) are for combining different colors or for reflecting the returning beam...
--DDL