Raw transactions mean that a private key never leaves your phone. The transactions are signed without the internet in your phone. Signed transactions are then uploaded to the network. This way of signing transactions uses popular hardware wallets. That's why this wallet is very safe to use.
High Deterministic mean that EthereumHD Raw Wallet is compatible with the most popular hardware wallets mnemonic seed(24 or 12 words).
You can put in this wallet your backup mnemonic seed phrase from Ledger Nano S or MEW and vice versa.