Question: 20-25 mm set-back or zero set-back? What do you like?

Seatpost offset should be specific to the user and bike's geometry.

It is how you can the attain the same end position on a 72 degree seat tube angle as a 73.5 degree seat tube angle.

This.

It is whichever gets your knees in the correct position relative to your pedal spindles.

The real question is what is the correct position? I am a KOPS guy but honestly it’s not clear if that is always best.

Time to see the assman! That’s gold, Jerry! GOLD!

I'm not a KOPS guy -- I like my saddle set back more than that. But again, for the OP, the choice of seatpost setback is about that saddle location, wherever it is.

Lets ask Rydabent

Agree, have to have confidence in what's under you. An example, my favorite road bar of all time is the 3T Superergo LTD (before that the Ergonova). There has been a significant issue with counterfeit 3T bars, especially back in the Ergonova days. I now only order directly from 3T. A price hit but a piece of mind savings. A reputable source is the only way I would ride CF bars.

That said when I mention flex in the Zipp SL seat post it's not in a concerning way, at least for me at 77Kg. I like the road feel vs their AL post.

Not to drive everyone nuts, but I've decided on Pro PLT Ergo bars and the Thomson Masterpiece for my seat post. I was ready to punch the "purchase" button on Enve Carbon bars, but just then my wife says to me "will those bars survive a crash?" And my answer was, "I don't know." I've had 3 wipe outs in the last year. Three were minor, where I was negotiating a sidewalk edge next to really soft dirt (my area is a desert) and the front wheel got stuck. I fell sideways each time and impacted the bars pretty heavily. Another crash was pretty significant. Not sure any carbon bars would not have cracked at some point. Thus, I decided to go with aluminum. Blasphemy, I know. But I don't want to go through several sets of $400 bars every few years. That, or maybe I should just learn how to ride a road bike properly. As for the seat post, the mechanic at my LBS (young, smart gal) advised that she only recommends Thompson posts (Masterpiece) and that she's never run into any binding issues with carbon frames. She believes our dry atmosphere has something to do with it. She also recommends a light greasing, although that appears to be counter the the accepted orthodoxy as to aluminum seat posts in a carbon frame. I'm almost there with all my parts. I'm having a hgeck of a time locating a new Force E1 RD in short cage. I can only find the medium cage version. I may have to get the prior Force version, as there's lots of short cage offerings all over the web. As an aside, I just received my Force E1 crank set. Really super nice. If I had to guess, I'd say that it's the equivalent of a Dura Ace offering. Really impressed by SRAM's stuff!

No. I have broken carbon seat posts many times. I finally gave up on them. They tend to break at the seat tube/post junction
1) I don't want carbon fibre splinters in the area that is at risk.
2) I don't want the fore mentioned splinters to have to be removed by some poor undeserving medical personnel.
3) Thompson seat posts are just great almost as light without the above risks.

Two piece seat posts of a variety of materials have been available from a number of big name producers for several decades. I'm sure that they would be able to absorb a lawsuit for some injurious component failure but have never heard of one.
Doesn't mean it didn't happen of course. Anything can break or be broken.
And steel posts are still in the market for the untrusting

How many times?
Which brand and model of CF seat posts?
How much did / do you weigh when they broke?
Did you use a torque wrench to install those CF seat posts that ended up breaking?

About a 50 g difference between a Cannondale Save vs. a Thomson (no "p") Elite seat post at 27.2 mm.

I've broken carbon seat posts before too. I find it helps to have an oversized, dual layer seat post clamp like https://a.co/d/aJQYU0P and line both layers with rubber. I think the pros even tend to use very low Nm tightness and just slap a second, undersized seat post clamp above the seat tube to prevent the seat post from slipping down despite the super low torque. Then you also have to baby it during use like making sure a lot of the post sticks down into the frame. Never pop it most of the way up.

I had a shopping bag with 6 broken posts in it. I threw it away a couple years ago. 2 Bontrager 1Specialized, the other 3 were all aftermarket.
kind of a personal question but let's just say over 2 bills. I'm not a little fella.
Yes. I use a torque wrench on all my carbon parts. The failure is from flexing at the insertion point. It literally grinds a groove into the back and eventually cracks.
50 grams I'll give back to the weight weenie gods for saftey as a sacrifice. Plus you can tweak those posts a bit to get the difference down some. Cut off the extra post etc.