Disabling the splash screen most likey wont be a regsitry entry you can modify, it would be coded into the app.
The reason why you maybe should not run older ZA, is it could have had a possible exploit discovered that could leave your system open. This is generally found and fixed in newer releases. That may be why someone was yelling at you not to use it.
Check on the ZA website and read through their changelog; if they publish it on the site, to see if and what security fixes have been changed from your version to the current, or another version someone recommends using.
If the only fixes where cosmetic, then keep what your using. If the fixes where major security holes discovered then consider upgrading. Since it would be pointless to run a firewall with a known exploit, you might as well not be running one.