You can move the echellogram anywhere on this field - but the relative locations of the boxes will stay the same. As with Taurus, the main reason for preferring the TEK over the LL device is its superior QE in the blue. Tests carried out in the coude room at the AAT, however, have showed significantly higher dark currents, which decrease with a time constant of about a day. This can have a significant impact on UHRF observers, where data is often binned over up to 1200 pixels. The main reason for preferring the TEK over the LL device is its superior QE in the blue.
Observers can either use smaller slits, or get better sampling of sky lines.
Observers of single objects with the LL can achieve quite short exposure times by windowing out the largely useless spatial direction.