PHP header redirect 301 – what are the implications?

The effect of the 301 would be that the search engines will index /option-a instead of /option-x. Which is probably a good thing since /option-x is not reachable for the search index and thus could have a positive effect on the index. Only if you use this wisely

After the redirect put exit(); to stop the rest of the script to execute

header("HTTP/1.1 301 Moved Permanently");
header("Location: /option-a");
exit();