I'm not sure this question was directed at me at all but I'll throw my 2c in.
I'm on stock sways on my M3P but I've upgraded to stiffer, adjustable aftermarket sways (with and without aftermarket endlinks) on two different ICE cars.
Most important: Get coilovers first, dial them in, and see how you feel about the handling from there.
Some cars have good, sporty factory suspension where simply upgrading the sways might achieve certain goals. (2021) Model 3 isn't one of them. The stock dampers need to go, don't bother with any suspension upgrades before that.
The Redwood coilovers have great handling balance with adjusters set the same front & rear. Very close to neutral. Adjustable sways give another tool for adjusting front:rear stiffness bias, besides swapping springs or damper adjustments, which can be useful, but you may or may not feel a need for that in this car with good well-balanced coilovers.
Stiffer sways really do reduce side-to-side suspension independence. I could feel that tradeoff in past cars. Did I regret the stiffer sways on my last ICE car? No not at all, I was very happy with the improvements on that car, for reduced lean and quicker steering response and somewhat better balance. But there was a tradeoff. Not terrible by any means but it was there.
My M3P on coilovers with stock sways has great suspension independence, and lean is very well controlled. For street use including tearing up the twisties I think stiffer sways would be detrimental overall,
on this car.
Track driving where you're constantly aiming for that ragged edge of the car's limits is different. You can adjust handling bias other ways, and you can use stiffer springs to reduce lean without sacrificing independence, but those have tradeoffs too and I could certainly believe that stiffer, adjustable sways might be worthwhile if you're tracking this car regularly. (I did track that ICE car of mine.)
Note that most every aftermarket sway bar I've seen (for any car) uses polyurethane bushings. That includes the ones I upgraded my ICE cars to.
In my experience keeping those bushings greased is a regular maintenance item. I tried seemingly everything - the grease the bar shipped with, marine grease, teflon tape, lithium grease, a couple other kinds...most of it worked but none of it lasted, the poly bushings would start squeaking again in a few months to a year. Now I was putting a lot of street miles on that car as a daily driver, and it saw some serious snow use in the winter, so depending on your usage perhaps poly bushings could go longer between regresses. I wouldn't count on it though.
Last warning, on the first car I upgraded sway bars on, I also put on aftermarket spherical endlinks. They were cheap ones and didn't last, got noisy within a year or two. I do trust Redwood to use much better bearings though than that junk I was using. (It was my first foray into any performance modding, I had some lessons to learn.)
Having that experience pushing this car to its limits should really help with figuring out what you want from suspension upgrades.
? JK! I already pushed the car beyond some of its stock limits on track my first go. I overheated my braking system in session 3 and had to pull into the hot pits. Luckily, I didn't boil my fluid and experience brake failure. So braking needs attention asap. As for stability and handling, I was left wanting more around the corners and felt generally unsafe when lifting over hills/bumps. My friend drives a Porsche 911 and BMW Z3 and both cars feel much more stabile at speed and while cornering. So an upgrade in that department would be just be nice to have.
