It works and it is simple and nice. But I found a problem in the code. (in class.cscf_settings.php)
In register_setting there is 'array_key' as option name which is common in some example codes. So it may interfere other plugins when option sanitize function called. (It will reset options of other plugins which use the same option name in register_setting.)
Please revise the code and rename the variables come from example codes.