Different model( number)s but exact same capabilities?

BU20 and BT30N, as much as SN208FB, TS-L633 and L632 seem pretty much identical in specifications. They also look identical.

What are the actual technical differences?

Chipsets, I guess. Maybe also OPUs

8x Slimtype and 24x Half Height drives are out for many years, there are no big differences in the specs, because there is nothing more to do for the manufacturers, expect lower cost for manufacturing.

Liteon also stopped to support DVD-RAM in newer drives, that´s the only think which is different in the specs