Based on available information, I would give "400 Last Verses" by Noel Rawsthorne a rating of 4.5 out of 5 stars. The book's practicality, range of content, and ease of use make it a valuable resource for worship leaders and churchgoers alike.
Two reasons: First, Rawsthorne published a follow-up volume— More Last Verses —which combined with the original brings the total number of alternate harmonizations to roughly 400. Second, organists talk. The slang term "The Four Hundred" stuck because it feels comprehensive.
This remains the best option. You can buy them directly from Kevin Mayhew or via Amazon/Sheet Music Plus.
These "naughty harmonies" are intended to uplift congregational singing and add a profound touch to the conclusion of a hymn without "train-wrecking" the singing.