System Lens is a program that sits on your Menu Bar and monitors your CPU resources usage. This application shows you a list containing running apps and their correspondent CPU usage and allows you to quickly shut down those tools in case you don't require them.
The utility constantly updates the aforementioned information, provides you with various monitoring settings, and doesn't use many CPU resources while sitting on your Menu Bar. On the right side of apps listed in the program's menu you can see the amount of CPU resources they use and you can use this info to determine exactly the reason why your Mac functions slow.
In my testing, System Lens worked flawlessly. In order to make sure the app offered accurate info I launched Activity Monitor (Mac's default app) and compared the details (they matched).
System Lens stays on your Menu Bar and lets you check the CPU usage info of any running app with minimum effort. However, your Mac comes with a default tool which is specifically designed for monitoring CPU usage (Activity Monitor) and closing applications.
Taking into consideration the presented facts, I'd say it's up to you to decide if it's worth installing this app on your Mac. You don't have to pay to use it, hence, you won't lose a dime if you choose to try it.
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