The 5 days is a pain actually, since to get the 1800 shards needed you'll need to either spend a lot of time (or consumables) or get lucky with the slayers.
I'm currently playing it safe going after the lower ranks, and hoping to get a decent rating through sheer number of attacks.
Biggest disadvantage shards have over Colo is the lack of extras to get from the boxes, which did help a lot.

All in all, I'll probably be able to get everything from Shards, but I do prefer Colo better.