I had a spice pull-out on my upper cabinets in my old kitchen, and it wasn't useful. The main problem was that a pull out that high was hard to see. It would have been much easier to see into a cabinet by either climbing on a cabinet or stool. The problem with a pull out at that height is that you can't see the top shelves very easily. This is hard for me to describe, but do a mock up of it and I think you'll get it.

That said, I would not to let 4.5 in. go to waste in a small kitchen. You may get more use out of a regular door (rather than the rack.) That would still allow you to put spices inside or anything else. The benefit of a door rather than a pull out is that once you get to eye-level (by climbing on something!) you can see in quite easily. You could also shelves to create a vertical cabinet for a few trays. You'd be surprised at how much you can store in a small space.

Depends on what would go there instead. Can you make another cabinet more useful by putting 4.5" more on one side? Would you basically be just using filler then instead? Do you actually have a bunch of those little spice jars?

Do you have a layout you could share?

I agree. I thought about the idea and KD didn't think a good idea for reasons listed.
If your kitchen is small- try a spice stack. My DH gave me one for Christmas. BBB has a smaller one and we bought the larger one on-line.
On iPhone in massive traffic jam with DH. Yes he is driving but needs my eyes.

The cabinet beside the spice pull out can be made bigger instead, which I think is more usefull, as it was it was a narrow 11inches...

Thanks everyone

A narrow 11" cab isn't very useful so would absolutely benefit from the extra 4.5"!

Love the spice stack! I have two. Thinking of buying a third.

Can you show a picture, mamasheshe? I have a 5 inch cabinet in my kitchen, and it's tight. I thought about a pull-out thing in it. It can't be anymore hard to see than it is now. The top shelf is almost useless. The bottom 2 shelves...one holds jar of peanut butter, the other the coffee container.

Here is a picture of our Spice Stack
Not a very good picture but it will give you the idea.
Rules -
-Something compact to hold a number of spices/herbs
-Ability to use original containers - I was so tired of pouring from one bottle to another.
-Easy to read the labels
-Easy to use

Just pull out the tray and drop it down - it stays in place - I still do so gingerly - but it is well balanced.
Downstream, I will label what is in the trays but still deciding what to keep and what to toss.

Depends on how tall you are. I had a lower cab pull-out spice rack in one kitchen and found it too inconvenient to use. I'm 6'2" and can usually see stuff on top shelves, so I might like an upper pullout spice rack.