Hercules is probably the most aggressive, allowing users to get themselves into big trouble by creating a situation where the system can't even boot. This is pretty rare, though. When I ran up the sliders in the Hercules control panel to their respective maximum, which visibly degraded the image and locked up the system, I was able to boot back into Windows and change it back after leaving the system off for a few minutes. Not all cards supply convenient tools to the user. While such controls offer freedom to end users, they can create support problems for the card companies.
Some users seem to have inflated expectations.
I've seen several reports of Hercules TNT2 Ultra cards being returned because they wouldn't run faster than 175MHz . Then there's the issue of memory speed. All memory is not created equal. It's a nice little tool that lets you tweak a number of graphics settings through a somewhat cluttered user interface. Whenever you start playing with clock rates, though, be very wary.