In addition to all of the differences between the other gauges and our standard gauge, outlined above, our slotted gauge has some very unique advantages. The slot effectively allows you to see how the cartridge fits into a tight chamber. This allows you to visually check that the shoulder is seated properly when you are checking the headspace measurements. If there is any other interference, you can see that as well. It allows you to inspect the entire profile of the cartridge, instead of just seeing if it sits flush in the gauge or not. And it makes it much easier to remove tight rounds.
Our gauges are designed to check against a tight SAAMI chamber so that what fits in the gauge, should work in any firing chamber. If you are not concerned about making ammunition that is within spec, or is capable of working in any gun aside from the one you are loading it for, you may want to use a different tool, or no tool at all.