Ponchos are great as long as you are walking in a straightforward manner on a trail. When you have to scramble, etc., a poncho can get to be a tad cumbersome...

Nothing is perfect in the rain, a fact brought home to me as I just now returned from an aborted trip to Santa Rosa Island, a bit drenched and sodden.

The poncho does q pretty good job of keeping your pack dry,but I would still bag critical items in plastic.