I appreciate the response. Unfortunately, the 1- and 2-star ratings for this, and similar products, on Amazon are off-putting. (Same for the otherwise interesting John Dow Industries Tire Taxi and Mr. You Tire Cover. Too many negative comments.)
Instead, I've gone in a somewhat different direction: a DIY project starting with a 50-gallon drum dolly (made of steel with eight rotating caster wheels) with 2,000 lb. capacity. With this as a base, there should be no problem with durability or breakage.
I notice that the price has been lowered (for the holidays).
I plan to put a wooden "cross" (probably two 2x4s) in the bottom with a flat "base" of plywood (either circular or rectangular). I may add a U-shaped handle secured to one edge of the plywood made of PVC, ABS, or even metal pipe; or not. (Once a wheel-set is stacked onboard, a handle may not be necessary.)
I had previously purchased some (Tesla, probably made-by-Kurgo) tire totes and some Kurgo tire felts, so the wheel/tires will be able to lie on their sides without damage to the rims.
This project will take a little effort, but not too much and it should give me a safe, secure, and durable 4-tire/wheel carrier that will allow easy mobile storage of my extra wheels in the garage.
Too many of the Amazon products are now made of plastic (commenters note that some used to be metal), and there are too many complaints among the feedback ratings. I'd rather spend ~$100+ for something that will last then to save money on a product made of plastic that is just going to break.
If the project succeeds, I will post the results with photos.