So, just back from a 20mile ride and I am suitably impressed!
The tl;dr review is the ride is smooth and luxurious and surprisingly quick, which I didn't realise till I got back and checked the Strava results.
Longer thoughts as follows.
It feels very solid and stable which is very confidence boosting and I hadn't been going long when I started noticing just how well it moved. I'm sure the stability comes from the frame and the chunky tyres, it's the sort of feeling VW tells you you get with their cars.
It didn't feel like it had the urgency that my Synapse has at times, but it just kind of flows.... How much of that is the frame, the wheels or what I don't know, having spent a few hundred quid on wheels I'm hoping it's got something to do with them though! I'm less bothered by the tyres now, at some point I might still get something a little thinner but they felt pretty good today and overall the bike handled rough patches of road and the canal path very well. They do give me that option to get off the tarmac more easily than something like the Marathon Supreme's I was eyeing up.
There are a few technical points I'll go back and compare to the synapse but the bars felt wider, and for me, with broad shoulders, that felt quite nice when on the hoods. It seemed to make using the drops harder but I think the way the lbs have setup the levers hasn't helped there, it was a bit of a stretch to pull the brakes from the drops. For what I want out of the bike though, I don't see that being a problem, if I wanting to get my head down and use the drops a lot I'd of gotten a different bike.
The gearing also seemed wider, which will be easy to check. There was one particular drop I've done a few times that I usually don't pedal for much of, partly due to spinning out a bit, partly due to focussing on keeping control

Today I felt I could pedal all the way and felt safer doing it. Previous 4 goes down it were between 28 and 32 seconds, today was 25....
The bottom gear was nice too, I think it's a 1 to 1 gearing 34:34 but I'd need to check, used it a couple of times and help spin up a couple of hills in a way I've struggled a bit more with before.
As for speed, I knew I was going along reasonably well, but I was still quite surprised when I got back and checked strava. I covered 9 segments I'd done before, PRs on 7 of them.... A good chunk of the route I did last week on the Syanpse, including all the segments I beat today.
One of the hills I've done a few times before though only 2 times I can compare which were 2:09 and 2:10. Today I knocked 10 seconds off.
Another segment a bit earlier on I've completed between 5:52 and 6:52 on 4 previous attempts was 5:16 today.
Only had a few down points and I think that's mostly to do with setup. I think I probably need a shorter stem, but I've thought that all along. I test rode a medium to see how that was, but it was far too small. The large feels right over all, but a little over reaching at times. I'm planning on going back for a bikefit and have said since I ordered it that I'd be interested in seeing if a stem change would help.
Also not too impressed with the way the lbs set up the brakes and gears. Quite a bit of travel on the brake levers, I tightened the back one but couldn't really work out what I was doing with the front, so even more annoyingly I ended up with different pull on each lever!
Any time I was in the big front ring I was getting chain rub noise, so that needs a little tweak and there were times when the cassette was jumping a bit. I'm assuming this is due to the lbs not quite getting it set up right, rather than an issue with Tiagra so can't mark it as a bad point of the bike.
That's probably plenty for now! I did have to stop at the butchers on the way round so the last 5 miles were with a few extra kilos on my back. I made it worthwhile by picking up a congratulatory steak and ale pie though, which was extremely tasty even if it did get a little squashed in my backpack.