What size did you expect?
Rack mountable would suggest it is going to be 440mm wide and 1U (44mm) high.
The spec suggests it will consume a max of 60w. From the spec: 100-240V~ 50/60Hz 0.6A so max current at lowest voltage 0.6X100 >> 60w. That will be when everything is working flat out - idle it will be a lot less.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
M H C
taurus excreta cerebrum vincit