The normal descent route is very complicated I have heard these days. When doing this route, wouldn't it be wiser to rapel the shield to camp these days?
Naturally, conditions in the mountains vary over the years. In 2011, the normal route above Garganta was in reasonably good shape again, with only one really steep section on the SW slopes, whereas the shield was out of condition: On the left, a big bergschrund blocked access to the shield, in the center, the ice was rock hard and I heard it was almost impossible to get a screw in, and to the right I saw a few seracs hanging above the face.
Given the relatively good condition of the normal route, I would strongly recommend it for the descent. Remember, you're going to be tired on the way down. On rappelling the face, one mistake can be your last. On walking down the normal route, with possibly one or two rappels along the way, there is at least a bit more room for errors.
Beware of inacurate guide books. There are actually 20 pitches on the shield using a 60m rope, instead of the 10 stated. It is not possible to get any V threads or on this type of ice so down climbing opportunities are limited unless you have many snow stakes or you can make snow bollards quickly.
At the top of the shield and before the summit there is a shoulder that can be used as an emergency bivoac. I strongly suggest taking a bivvy bag with you unless you are in top level condition and the weather is perfect. I didn't and lost a few toes up there. Also, cigarette lighters will not work at this altitude, so bring plenty of water.
There are stakes with flags marking the regular route on the way back. Beware of a widening crevasse in this flagged area that needs to be jumped over while roped; some of the guided parties in 2012 were turning back at this point.