If the code is working for you on your site, feel free to use it.
However, it has been rejected as a contribution because it is destructive (deletes all tax and zone configurations, regardless of their use) and ignores built-in Zen Cart zone and tax calculation features. In its current state it is way too dangerous to be made available to shopowners who don't have a solid understanding of the risks of using it as well as PHP programming in general.
You seem to be content that it is meeting your needs. As such, I won't recommend that you stop using it. However, take note that you will not be able to use Zen Cart's built-in zones features for anything, including taxes, shipping/payment mod restrictions, address restrictions, etc.
We do not mean to discourage your contribution efforts. Please understand that it has been rejected specifically for the reasons stated.
If it's any consolation, the v1.4 release will most likely contain the ability you're looking for by the time it is released next year.
.
Zen Cart - putting the dream of business ownership within reach of anyone!
Donate to: DrByte directly or to the Zen Cart team as a whole
Remember: Any code suggestions you see here are merely suggestions. You assume full responsibility for your use of any such suggestions, including any impact ANY alterations you make to your site may have on your PCI compliance.
Furthermore, any advice you see here about PCI matters is merely an opinion, and should not be relied upon as "official". Official PCI information should be obtained from the PCI Security Council directly or from one of their authorized Assessors.