Thought I'd toss in my two cents, since I think a lot of bad answers have popped up on this thread.
1)
Macs are more secure than their PC counterparts, but feel free to wholly ignore people who say Macs don't get viruses. It's more difficult to write viruses for Mac, it's more difficult for Mac users to inadvertently install/run malicious programs, and the market for infecting Macs is muuuch smaller than the one for PCs. macOS is still just an operating system that can have its safeguards/protections circumnavigated by malicious actors.
Do they need an active virus scanner? Not really, as long as you browse the internet with discretion, keep stuff up-to-date, and are wary about launching/opening files. However, in a business environment or where multiple users will have access to the machine and the like it's often a good idea to have the safety net of an antivirus.
2)
a)
Some AV programs do "spy" (typically disclosing what/where they glean) on users and it's worth looking into which companies do that and in what way. Most "spying" is more diagnostics & product usage (telemetry- which helps the products improve) as opposed to marketing snooping. Investigate which sort of phoning-home the AV vendors are doing.
b)
A Sophos staff member had this to say about the user account:
"
We automatically create an account called "_sophos" when we install the software. Its full name is "Sophos Endpoint". If you run the uninstall app we will automatically remove that user from your system.
We needed to do this because we no longer run all of our software as root, and we didn't want to "borrow" any of Apple's standard accounts. We have intentionally disabled login to the account, and limit its access to the rest of your system: it can't do anything that requires privileges, and it cannot access the private data of any other users on the system. This is a fairly standard security technique for UNIX-y systems (which includes Mac OS X).
"
c)
Avira is very simple and isn't a good choice for anyone wanting thorough management controls.
d)
The common free AV solutions for Mac have real-time protection (Avira, AVG, Avast, and Sophos). If you decide to go the route of having an AV on your Mac, seriously consider using a free, AV-only product as the extra features of the premium versions ("system optimizers", VPNs, ect...) are often redundant, bloated, or unnecessary.