Yes but you must note that ClearOS 6 has gone End-of-life and is receiving no more updates. If any vulnerabilities appear, they will not be patched.

Can I use the Bandwidth manager in CleaOS 6?

It is possible to install the old bandwidth manager from the command line as you have found out. I have absolutely no idea if it works as it was never properly released for ClearOS 7.x and probably was not tested.

Hi, thank you for your response, I found a way on how to download and use the old Bandwidth Manager, is it still functional? Because, I followed the steps in the Documentation but it seems it's not working.

The old bandwidth manager from 6.x no longer exists. Now there is a Bandwidth/QoS manager which works differently and it is no easy to make it limit bandwidth. It allows you to allocate priorities with the lowest being 7 and the highest being 1. Any device in band 7 is allowed the full bandwidth if nothing else is using it. However if a device with a higher priority requires some bandwidth, it gets it in preference to a device of priority 7.

It goes on the the thinking "if no one else wants it, why limit the bandwidth of the lowest priority device".