There is no reason. From their Website:
SafeSquid™ , as the name suggests is inspired out of the name of Squid.
Squid is an excellent Internet proxy server built by an entirely different team of people
and maintained at
http://www.squid-cache.org
SafeSquid™ is functionally quite similar to Squid, just the perspective and execution is different.
SafeSquid™ basically looks to address, the need of an web-gateway from the security perspective.
SafeSquid™ is a complete Content Filtering Internet Proxy with intrinsic capabilities for filtering malicious content.
SafeSquid™ can be used independently;
- or in-conjunction with Squid, as just a content-filter!
The name SafeSquid™ was therefore set by the product managers just to underline the analogy.
There is no relation between the two. They openly admit that they names their product "SafeSquid" to confuse people. A dirty trick indeed, but it is likely that they will get away with it, since the Squid name is not trademarked. They may even try and force Squid to change its name now, given that they have trademarked "SafeSquid".
In any case, there is no need for you to uninstall Squid and install a newer, untried, non-Open-Source proxy. It's unlikely that they even have an OSX version anyway.