Some initial impressions:
It's fast. It starts up and comes out of sleep mode far quicker than the fp L, the autofocus is very responsive, it has a large buffer, writing photos to the internal storage is quick, and playback is fast.
JPEGs are excellent, just like the fp L. The DNG files contain a camera profile and this produces good colour (the fp L's DNG profile produced somewhat dull colours and cyan skies) when processed in an application that will recognise it (I use Iridient Developer) without the need for specific support for the camera.
It eats batteries, just like the fp L. Unfortunately Sigma UK are currently out of stock, plus the batteries are ridiculously expensive (£99.99, the charger costs £139

).
The playback and option buttons are both conventional buttons and touch sensitive, so pressing the playback button activates playback mode, but touching it shows you the last photo taken; similarly pressing the option button takes you to the options screen, while touching it displays the status bar with the battery level, time and remaining photos.
You can directly attach a USB C SSD to the camera and back up everything on the internal storage, with the option to clear the internal storage after the copy completes. So no need for a computer to back up your photos and videos.
The black finish looks really nice but it tends to show fingerprints. The sharp edges aren't really
that sharp, plus the front left and rear right corners are bevelled so they don't dig into your hands.
One oddity: Auto ISO is behaving inconsistently. I've got it set 100 to 6400, but it sometimes refuses to go below 400 (the sensor is dual ISO, 100 and 400) and I'm not sure what the cause is.