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!