Product review (5 stars): Lesson learned:  Order this at the same time you order a replacement tub seal washer.  The old one might break when removing!
When you've been so frustrated at your old tub nut, that you wind up using your spanner wrench with a sledge hammer (instead of a regular hammer, since it won't work) to remove the old nut, you might find that the older, encrusted/rusted tub nut might might have a crack in it.  Thusly, comes Amazon to the rescue.

My nine-year-old nut was so encrusted that you couldn't even see the word "loosen" on it.  Attempts to use the spanner wrench with a mallet/hammer going clockwise (yeah, that's the way you loosen this) proved fruitless to dislodge the old tub nut.  The sledgehammer was then broken out, eventually loosened that old tub nut, and allowed me with proceeding to replace the tub seal (which is all I really wanted to do in the first place.)

This nut, as far as nuts go, was easy to put on with the spanner wrench.  A regular hammer on the spanner wrench going counter clockwise until it didn't budge was all it took to tighten it.