The ease of use, it's free so there are no hidden costs that I can see! It does what you would expect from an anti-spam/anti-malware solution but also has some nice features for privacy too if required - like being able to set up rules per user account (or group) rather than having all accounts treated equally by default when using "block mail" as such. There have been occasions where my work emails were blocked in error or due to misconfiguration resulting in me not receiving critical messages until later hours after they should've gone through. Nothing major really, just something we'd prefer didn't happen unless necessary. We're solving our own problems around security at this point anyway though, hence why I'm giving them positive feedback here :) Anti-Spam / Antimalware software used in conjunction with business grade firewall.