yes. It's best in many tests and I also personally find it the best too.
It gets it worst review for its user interface but personally I like it. It's simple, works fast and doesn't drain much resources.
But I don't know if it's worth paying for extra features. Depends on what you need. It has the same engine and detection rate. However for firewall and some other stuff you have to pay more than 20 - you have to buy "Security suite" which is more than premium.
Premium gives you some email protection, faster update download servers (free are fast enough though) etc.
However the free antivirus itself was enough to keep me virus free. From time to time I get a pop-up that I have a virus, I delete it and have no problems. Since I use it I never had any problems with Viruses.