We have the Armada Pro 800 and your right it is a great tool. The 521's work well but for some reason we just have better luck with the 800. My guys like it and they are comfortable using it. I like the fact that you can keep it charged at the shop or plug it in in the truck. It seems like every time we would go to use the other locators the batteries would be dead. Probably from employees leaving them on. Once I find something I really like, I stick with it and put them in each truck.