Checking AC charge-Is it this simple??

Was in Walmart tonight and was looking at the freon supplies and they had a kit that had the gauge and hose hookup. I know nothing about working on the AC system.
The directions were pretty straightforward. You hook the hose up and read the gauge and you either have a good charge or you don't. Sort of like checking the air pressure in a tire.
It told you that if you are low then add the contents from the freon can and add enough until the gauge shows a good charge. So is it really this simple to check your AC condition? How reliable are the gauges that come with the kit? Thanks!

Yep, it's easy and I've had great success with those kits. I rec you get the gauge with a trigger that fits on the small cans of freon because you can reuse the gauge later. If you get the tall cans with the push tops then it's a one time use then discard. Those gauges aren't made to be taken off and used on another can of freon.