Has anyone out in the real world been able to quantify whether or not the square downtube is actually causing significant drag? Meaning, does the riding dynamics on road feel draggy? Can you actually tell?

I spent a significant amount of time riding side by side with friends on flat terrain, and as someone who pays close attention to power data, I feel confident that this bike doesn't come with an aero penalty. Based on what I've read about aerodynamics, the downtube is positioned in the 'dirty air' created by the front wheel, so having a slightly less aerodynamic shape doesn’t significantly impact performance.

I have used both the ryet full carbon saddle and the plastic base one.  All have held up very well, and have continued to buy them.   In one instance I ran it with an elita one seatpost that just used the turned metal rail clamp.  After it slipped a couple of times I over torqued it, and it worked fine for a year but I compromised the carbon rails (user error/less than ideal design).   The saddle eventually failed while bunny hopping and landing hard on the saddle.  For cx/mtb, I err on the steel rail version.

One takeaway from the grading scale is the sample rate for QC.  I know everyone who drops a couple thousand dollars on a frame would love to believe it has been finely inspected in the factory, but the reality of QC is that you need to define a sample rate and have a process that is capable.  A more frequent sample rate is expensive for the labor to check, but it lowers the probability that process went sideways during the production.   It doesn't eliminate the chance that problems happen. 

I hope LightCarbon addresses this frame and replaces it.  I do think a lot of brands buy with smaller QC sample rates but rely on after market warranty to take care of issues when they arise, or they put in their own post-production inspection to return frames not up to brand standard (but this seems unlikely to me/or at least is a sample rate that is not 100%).

I am both excited for a Hambini video on this frame.  From my experience, if was a fantastic build and has been a great bike, and I would like for its internet cred to be maintained.

One update, while I don't have access to any sort of formal data, all my intuition and imperfect benchmarks on aero has been good despite the shape of the downtube. Riding side by side with others that I know their pm and my other bikes, this one has held up great.

FYI - the ZRace XG calipers have been working fine at least for road. Nothing wrong with LTwoo calipers and they might be better if aero is a priority, but since I focus more on climbing I prefer the weight drop of the XG calipers. I've been using them on both my mechanical Ultegra and ER9 bikes with no problems so far.

My experience with the xg calipers was fine for the first installation.  But upon trying to rerun lines a second time, I found the threads to be very soft and stripped them trying to crush an olive.  That and the ability to block the brake fluid with the hose placement (shown in trace velo video) was also annoying.

Took me a bit longer to make this post.  Overall experience has been really good.  The fit of everything was spot on. Full build came in at 15.2 lbs without pedals (size 52).  For being that light, I am also surprised at how stiff it feels in accelerations.  My order was handled well and had great communication. I really like the color but it is more purple than I expected, but it looks great.  You can see in the sunlight it has the orangish chameleon, but the purple is the dominant color. Paint selection was LCB-02HS. Current setup is gp5000 28mm, but have a second wheelset with 32mm gp5000. One bummer is the width of handlebar options.  I went with the 40 x 110 handlebar and I have been running narrower bars and would have selected narrower, if available.

I will quickly address some of the items on this thread:
My frame has a drain hole under the BB
I will say that the layup feels pretty thin below the bottle cage on the downtube.  It is a larger tube size, but the wall thickness feels thin.
Brake caliper mounts are faced
Rear thru axle does require more torque than other frames (but doesn't appear to be any thread damage, so I don't know, not really an issue to me, but a previous poster described this).

I had to cut the seat tube to get my fit right, but just 1/2" or so.
I also ran into an issue with the seatpost clamp.  After riding I needed to adjust, and upon retorque the clamp to 6nm something with the pins that hold the bolt broke.  I have contacted LC and will update with how quickly they respond.  I am pretty sure their clamp is a tried and true design across other frames, so I am not quite sure. I want to tear it apart to see whats going on but it is kind of a captive part.

52

What size did you order?

52cm