I'm considering using this redirect to create internal redirects for 50,000 users or more. Will this slow my site down?

Unfortunately, I'm not sure that will apply in my case as each url must point to a specific users page (sort of like a Community Builder Profile, except I'm using a custom CCK). With this many users, I may need to use a url shortening service like Google or bitly, but I was hoping that I could create aliases on my own domain (much better for branding our products).
Please let me know if you think I'm missing something. Thanks for your quick reply.

Forgive my ignorance. I think I'm understanding you, but I'd like to be sure.
This is my scenario:

Let's assume that selfget has purchased 4 animal ID tags for each of his pets, and each one has a QR-Code url that leads to the online profile for that particular animal. An actual profile for one of selfget's pets may reside at /horses/5/ABCD, where "horses" is the animal category, "5" is the article id, and "ABCD" is the ID for the tag itself. The shortened url should be /ABCD, and this is the url that will be printed on the tag that gets issued for that animal. Thus /ABCD should be directed to /horses/5/ABCD.
Similarly, animal two might be /horses/6/ABCA and the shortened url would be "/ABCA". Every tag is unique. I think you're saying that I could lookup the article id and tag id using macros and use the same rule for every animal. If true, I assume that it wouldn't matter how many animals I added to the database. Am I getting this correct?