Did my first ride on it yesterday (only an hour because I'm recovering from an accident):

-It's stable - not in annoying way, but definiteley not nervous like a Giant TCX or the Factor O2 it replaced
-It clears 45mm tires (when using a GRX Di2 front derailleur) but only just. With a 21mm internal rim these tires (Schwalbe G One RS) are quite voluminous. I'm afraid I'll have to size down or dremel down...
-It's quick enough (or I am), averaged 33 kph
-The slipping seat post as someone mentioned is also a problem for me, I thought i'd have done it up tight already but it still slipped about 1.5cm during the ride.

All in all I really like it, can't wait to go out on an actual gravel ride with it now!

For me the alloy top part was sticking out wider than the fork, so I sanded it down until it was flush. Otherwise the stem wouldn't slide over the top of the fork.

My build is almost finished, just received a GRX Di2 front derailleur so that a 45C Schwalbe G-One RS fits (not much room to spare but i wouldn't ride these tires in muddy conditions anyway). With a Dura Ace Di2 there was about one millimetre to spare, and now it's maybe 3-4mm. The only challenges so far were the expander and getting the headset running smoothly, a thin spacer underneath the top cap solved it.

Both the pictures and some reviews indicated it would be a genuine Thomson post. Aliexpress agreed with me on the dispute, so apparently I had a case there.