IN THE VERY END, they're quite smooth, functionally indistinguishable, really as good as the name brand stuff, The only difference, they're ugly.. And I'd assume many people won't be able to swallow that pill..
Considering they're on the underside, I think it's a pretty easy pill to swallow.
With all that extra material, have you considered experimenting with other shapes/larger skate surfaces?
Well... Here's how I see it..
The less surface is in contact with the pad, the less the friction.
Increasing the teflon surface is not to reduce friction, increased surface is done to reduce the mouse's Roll and Pitch...
Since I myself am a high-sensitivity , finger tip user.. I do not exert much downward pressure, and I don't move the mouse hard and far enough to generate much roll and pitch..
So, FOR ME, I feel it is ideal to reduce the contact surface.
But if you're a low sensitivity, or a palm gripper, or both, Then surely more surface would be beneficial..
To my understanding of friction physics (F = μ mg), surface area is completely independent of total friction. This is due to a larger surface area distributing it's weight better. So for example something with twice the surface area will only exert half as much force per square inch, making it exactly the same amount of friction as something with half the surface area exerting twice the force per square inch. This relationship only breaks down once you get to surface areas small enough to dig into one another (a blade for example).

Naw, Dawg, You're thinking of the simplified model of friction.
Overall, if you want to argue the mechanical side.. yea.. it's good enough, and you're correct ..
However, the reality is a gamble..
Every instance of friction is unique and potentially incalculable...
There's a possibility that more surface means the same amount of friction, there is a possibility that more surface means less amount of friction, there is the possibility that more surface is an equal amount of friction..
We have no ways to perfectly determine the above 3 questions..
Therefore, if I look elsewhere... Fundamentally, I can compute and have a greater possibility of knowing the friction of small surface area..... whereas when that area increases the possibility is less.. (as i run out of computational power)
Now, you're going to say, well, the truth may be, that you have 0 possibility of computing either of the areas..
Sigh............ you see why this becomes a gamble..
So, I must make a decision based on inaccurate approximation no matter how deep I go..
I choose to end it at the first round of potentialities.