Let's be perfectly honest, while the LUCAS device can certainly do effective compressions, it's not "perfect CPR everytime" and you certainly can't just sit back and watch.
It's our standard of care that we use a LUCAS on every arrest (provided the PT fits the LUCAS criteria) and I find that unless you're paying close attention to the placement of the LUCAS, even with all of the straps attached, the device will still migrate and the plunger will not be in the correct position during patient moves or during transport in a bumpy ambulance.
I don't like moving active arrests with CPR in progress anyway, but on a busy code, the potential to forget about the LUCAS is there and unless the medic is keeping a close eye on things, including the quality of compressions and assuring correct device placement, the LUCAS may become ineffective quickly.