I found the wheel gauge on the Kadee tool a bit tight. So if you find the back to back spacing on an axle a little wide, don’t bother adjusting it. I did and I had derailments with cars that tracked well before. If it is too narrow, move the wheels out to at least fit the gauge.
Unless the track gauge it constantly held 90 degrees to the track, it could be misleading. It’s alright for spot checks, but a good gauge would have provisions to prevent skewing. Push a plastic freight truck down a track and it will quickly find the narrow spots, or shallow frogs.
The wheel gauge does not measure the back to back, it measures the distance between the edges of the flanges, and depends heavily on the thickness of the flanges.
In other words, it does not measure the right thing, and it does a variable job of it.
I say do not use it. If you wanted to make it useful, deepen the slots and measure back to back, but you have to make the slots meet the standard you want. I prefer the Aristo gauge, it has min and max back to back, and closely tracks the NMRA and G1MRA standards.
The G1MRA standard for back-to-back minimum is 40mm. A lot of Aristo locos have a back-to-back of 39mm, which is too tight for some brands of commercial track not made with code 332 rail. Just be aware of that if you plan to take your equipment somewhere else to run.
The Kadee gauge is crude at best. I have never used it except to see if something is WAY OFF. To my mind, the best tool is an inexpensive set of (plastic even) calipers, because they have so many other good uses.
I cannot comment on the Aristo gauge itself, having never seen or used one.