MetaMask is an Ethereum based and easy to use browser for all transactions using Ethereum contract address and Ethereum related coins.
MetaMask there is no need to the blockchain because features can be use to interact with Ethereum related website to access and enable any transactions.
MetaMask is very easy, simple to use and requires no registration, private key, no KYC in any server, instead they are on browser and protected.
There are doubts about metamask from beginning but as I started using I saw it's safe and reliable very easy and simple to use.
MetaMask operates strictly on only Ethereum blockchain.