I've used the app for more than a year now, and I'm not happy with it. The main problem is that it is SLOW. Part of the reason that I can actually observe is that when I click on a running process, it goes out to its database of processes to show me what the process is for. Now, that would be useful if I actually wanted to know for a specific process, but in general I already know and I don't want to waste the screen space or the lookup time, which is particularly annoying if it can't find it (Firefox!). There is no way to hide that pane and stop that behaviour; I have to wait for it before I can kill the process, even when right-clicking on the app to act from the context menu..
I have no idea why else it is slow, but whatever it is doing is a whole lot slower than using the comparable commands from Terminal, and it eats CPU while doing it. I have to force-quit Processes more often from the dock than I can use it to quickly kill a CPU-gobbling process.