':back' is mapped to 'H' -- in correspondence to the usual Vi/Vim paradigm to move the cursor with the home-row keys, hjkl. ':open' is naturally mapped to 'o' and drops you into a tab-completable shell. ':tabopen' -> 't' and so on.
The key part, as in Vim, are /not/ the mnemonic, highly effective shortcuts.
Rather, it's the modal workflow that Vim and it's spritual descendants bring to the table.
I'll leave it at that (sounding like a damn preacher already).
 Now that I've looked at it, it becomes clear that they're selling rather directly to Vim-acolytes. Pity, perhaps.