rick, I count either 17 or 19 slices with that butter slicer. I think the thing slices into 'pats', not tablespoons.
A useless item I own is a pressure cooker. I don't use it because I'm always afraid it will blow up. Also, I never use my crockpot, either. But someday, which I've been saying for over 2 decades now.
Something I was given that I thought would be useless is this:
a cherry pitter. Now I've never used it for cherries, but it works great on olives, so it's gotten way more use than I ever thought it would (because I thought it would never get any use).
Now for that lady's grilled cheese pan, I'd use it for a Potatoes Anna pan.
Improvise, adapt, overcome.