When you say MacFee...I believe you are referring to McAfee.
According to BT Customer Support, they offer BT NetProtect Plus anti virus
which actually downloads McAfee.
Although McAfee is as good as any other well known anti-virus program, it requires numerous services and running processes that consume a lot of system resources and often results in complaints of high CPU usage. Anti-virus software components insert themselves deep into the operating systems core where they install kernel mode drivers
that load at boot-up and create files/folders/registry entries in various locations. If you do a Google Search
you will find there have been numerous complaints about it affecting system performance.
Further McAfee products, like Symantec, are becoming difficult to remove and remnants are often left behind which require the use of a special removal tool, otherwise you may encounter problems installing a replacement anti-virus. To be fair, other vendors also recommend using removal tools for the same reason. Those issues plus the cost factor are the primary reason many folks look for a free alternative. IMO, McAfee is better utilized in an Enterprise system environment
protecting many client computers.