Looks awesome, well done!
The whole thing looks stiff indeed. That seatpost is scary, i dont see how anything can deflect, so good thing you have fat tyres and steel spokes and not carbon ones. Make sure you follow recommended PSI and dont go italian by putting 100psi in 32C tyres. I have italian friends, i stopped trying to explain to them that it makes no sense to over inflate big tyres. Good, big tyres at the right PSI completely change a bike.
Such a chonly boi will never be light, if you check out triathlon forums, you will see people's bikes are super heavy, comes with the territory.
The bike looks like a sail, for sure it's going to be awful in cross winds Be careful when you see trucks, you can get pushed or sucked in hard on something like that, try not to die.

Thanks for taking the time to post, it's great to see Chinese TT frames.

Really great to see updates on this, the price of TT bikes at the moment is painful. I would love to know the actual weight of this and if you manage to sort the rattling / things getting loose

I also ordered this frame a few weeks ago, still waiting for it to arrive. I also asked them to add some bento box rivets to the top tube which they said yes to, so that's an option.

Is there any way of routing di2 cables down the extensions? I was assuming that there was an exit hole somewhere at the bottom of the extensions but I cant see one

You should make a list with good/bad sellers for us .