The Petzl Gradistep Etrier is the lightest etrier style aider we tested. It is great for rock climbs with only a little aid or alpine climbs where you want to travel light and are using sturdy boots. The coolest feature is the little bag that the aiders fold up in. This is not recommended for any aid lead where you will be standing around for a while.
While this is a very cool aider, it has a very limited application range. If you are doing a lot of speed climbing on mostly free big walls, this is a great tool to have. But usually I would reach for the Petzl Wall Step Etrier instead. The WallStep is bulkier, but its not actually that heavy and is loads more comfortable. Or if I wanted an alpine aider, I would lean more toward the Metolius Alpine Aider that is more versatile and $15 less.