The ease of use is great, anyone can pick these up and generally find there ring size
The package they came in was fairly good, and sturdy.
The ability to remove it from the metal ring is fairly easy and just requires you to spin the part
Cons: They aren't perfectly accurate, they come pretty darn close for some cheap amazon sizer but they can have 0.5th of a size from true size difference
They are also quite loud handling them in any context so if you're fairly sensitive to sound, this would be an issue
Overall: Great value for price, but if you are buying a wedding ring or something else that is expensive i would get a different ring sizer, and or check out a shop so they can size you professionally