I have the Hornady cartridge case headspace gauge, a Wilson .223 case gauge and the JP .223 Chamber Case Gauge.
So here is the problem, a fired case will not fit in a Wilson or JP gauge so you don't know the fired length of the case to setup your die for proper shoulder bump.
The JP .223 Chamber Case Gauge works great for checking the loaded cartridge doing a final check.
Below is a fired case in my Hornady gauge.
Below the same case after resizing with .003 shoulder bump.
Bottom line, I'm 65 and have chronologically gifted eyesight and find it very easy to see the digital display on the calipers. The Hornady gauge makes it very easy to setup your dies and not over resize your cases. And the JP .223 Chamber Case Gauge is good for the final check to make sure it will chamber.
I buy a lot of once fired Lake City military brass, and it is sized with a small base die to ensure it will chamber in three different AR15 rifles. Also commercial .223 cases are not made as hard as 5.56 cases and can cause extraction problems f not sized properly . On top of this resizing dies do vary in size, as a example I have a standard Lee die that will push the shoulder back .009 shorter than my GO gauge. And this same die sizes the case smaller in diameter than my RCBS small base die. So having more than one type of gauge comes in handy to solving problems.
If you are young with good eyesight you could get by with just the JP .223 Chamber Case Gauge. "BUT" just remember there is only .003 difference between the top and bottom steps. And a resized case for a semi-auto should be .003 to .005 smaller in diameter than a fired case and .003 to .006 shorter than the chamber for reliable extraction.