Apart from the fact that MetaMask is an altcoin wallet not a "shield"; technically you should keep your bitcoin offline so that getting your online system infected wouldn't affect them. And if you want protection install uBlock Origin and a decent Anti Virus on your system that has net protection.
I know a lot of people here dislike Ethereum, MetaMask does have a feature of
potentially showing a warning if the user opens a phishing site, which I don't think uBlock Origin has that feature.
There's this one plugin that's made exclusively for blocking phishing sites though, so it should be a better pick than MetaMask. I forgot the name of the plugin.