In practical sense No Antivirus can protect your Tab/Smartphone from Malware or Virus completely.
Almost all known Antivirus company give similar layer of protection for Free[Android/IOS]. It can protect your system from getting Risky webpages,Small level malwares,Spam mails. With the paid version they give you just extra features.
Secure wifi means that it requires a password to use the specific wifi connection at that location.
Just because the connection requires a password in absolutely no way means that there is any magical safeguards that prevents a website or email or file from infecting your device the same way it infects every other device.
In regards to what protection you need that really depends on you. Do you download apps that are not in the play store, do you download offbeat education or game apps from play store, do you download/play files from torrents or other non-legitimate sources, do blindly open emails and click on links without consideration for security? All of those activities would put you at higher risk for an infection.