I carry an Exped Bivy Poncho
, but in addition to a tarp. I do that in case I need to set up in the rain---which would mean taking off the poncho while its raining if that's my only rain shelter.
Its 6" shorter and 2" wider than the one you linked to, but has snaps on all sides which would allow a larger shelter to be built if two individuals are traveling together.
To give an idea of how big a shelter it would make:
Personally, I look on a poncho tarp as more of an emergency shelter.