I haven't read this but I adored "Modern English Usage (1926) as a child.
Apt/liable, "quite all right", and hyphens come to mind.
But the slightly mad suggestion about "that" for "which" has wreaked a bit of havoc in the U.S. ever since the slightly mad Harold Ross imposed it on the New Yorker., whence it passed into general use. People who toss out wild ideas should remember: the Americans are listening, and prone to enthusiasm.