I have used both types of waxes. The "authentic" or "typical" wax sticks and The "glue gun sticks".
The typical wax sticks when harden, will break. While the glue gun sticks when hard, are pliable.
When I used the typical wax through the mail, they had gotten torn off. The glue gun sticks went through fine. I don't know why it makes a difference to the postal system, but for me, it did.
I use the glue gun sticks for mailing and the "typical" wax for hand delivered.
The glue gun sticks come in an endless array of colors.
If I am only sealing a couple of envelopes, I will melt the stick over a flame...not IN the flame... just over it and twirl the stick till just before it drips, then apply it to the envelope. More than a few, I will use a low temp glue gun.
I have never used the pre-made "stick on" wax seals.
Hope that may help some.