(5/5)
The documentation is very complete. The author gives examples of how to use the snippet and he explains the snippet's function and objective.

     (4/5)
It's very simple to use the snippet. Using $encrypt('text'), the field 'text' will be encrypted and you can revert the result using the same command.
 
An example given by the author:
 
//VAR %text thisismytext | VAR %string $encrypt(%text) | echo -a 04 %text 05 $encrypt(%string)
 
The value of var %text is 'thisismytext' and the value of var %string is 'thisismytext' encrypted. The result will be: "thisismytext thisismytext" (because in echo command the var %string was encrypted and return to the %text's value)

Not rated
Design is not rated for this, as it's text based.

It's a good snippet to substitute the $encode/$decode identifiers.