Hm, commonly, on lower performance CPU's like the K6-2, only Guardband Clipping will have a reasonable effect on performance.

This is also only true, if the rendered scenes contain enough Geometry to Clip, so the setting shows a noteable (e.g. Benchmark scores) effect.

HSR should only work under OpenGL, with Quake3 based Engines (but is reported to have significant Visual Artifacts).

Anyway, regardless of Driver used, most settings do not have massive effect, they're just small tweaks.
And if the Card is already waiting for the CPU all the time, tweaking the Card won't have a big effect...

The biggest difference is probably Visual Quality (e.g. Edge Antialiasing, 22bit Post Filter etc.)

I admit the last Time I used it, was with a Voodoo2.
(that's where it originated, as the very first step towards Antialiasing 3dfx ever made)

But there, this indeed worked very well.

If it does not work in a 3rd party Driver, that means that the Direct3D Core Driver is incompatible with the Tweak, and the Driver Author didn't notice or care.

But it does work, I've seen it myself

It should work in any Direct3D application, but the Driver needs to be 'correct' about it.

It's probably best to spot in low Detail Games, where each polygon is still a bit distinguished from the other, and has a high contrast.

Back in time, I tested it in 3D Winbench, which did a good job of giving still images for comparison (Image Quality)