Fish's Smart Aider uses the a simple design that has led to thousands of successful big wall ascents. Chris McNamara used these for his first 10 big walls and loved them. Fish Smart is the most durable aider we tested. After two decades and 30-plus walls the pair Chris first used are still going strong. He changed to different aiders only when he found a pair that had the top sub-step and later when he started using aiders that had larger steps with more reinforcement. Overall, for $47 (for a pair) they are an amazing value.
If you are counting your pennies (who isn't?) this is the most aider for your dollar by a large margin. You can buy five of these for the price of a pair of Petzl Wall Step Etrier. With unlimited funds, you might prefer the Metolius 5 Step Aider or the GradiStep for an etrier style aider. But the Fish Smart Aider will get you up any wall and have the advantage of being lighter than most aiders on the market. Also, if you are one of those people who doesn't like the urethane-coated aiders, this is the best etrier style aider to get.