I was a bit hesitant to purchase RLM as I was fairly sold on Macaw, but after comparing the two and discussing the pros and cons of both, I broke and went with RLM. In the first few hours I owned it it helped me finish and launch a project I had been working on. I was struggling with breakpoints and getting my menus to work properly on a mobile device -- RLM made is super easy and the support I received from CoffeeCup has been (as Davermont mentioned) quick and friendly.
The main reason I went with RLM is because of its Grid System as opposed to Macaw's Grid Guideline's. I can only see the Grid System improving with future releases. CoffeeCup has a good article on the difference here: http://www.coffeecup.com/help/articles/grid-systems-and-frameworks/
All said, I'll still be using my other tools (Coda, CodeKit, and Sublime Text) as RLM can't do everything. But, I like what it can do and its helping me getting done a lot faster.
I highly recommend giving it a try.