One big advantage is the runtime efficiency. Merb processes use less then half the ram of a rails process and can serve 2-5 times the traffic. This means you sa

One big advantage is the runtime efficiency. Merb processes use less then half the ram of a rails process and can serve 2-5 times the traffic. This means you save a lot of money scaling your app for traffic demands. Merb also does not lock you in to a specific way of doing things. It's very easy to bend the framework to your will. Rails is great for the 80/20 rule. Rails will take you the first 80% faster then any other framework. But rails will make it super difficult to get that last 20% and will cost you double the hosting fees(over merb) or more when you have to scale.