Just ordered the Tubus Grand Tour rack. 130 EUR is not too bad since I expect to use it for a long time.
The idea is to use the gravel bike as a touring bike on multi-day trips. Kind of a do-it-all bike. I might put a front rack on it as well.
The main factor was that I liked the design of it more than other racks, in terms of how I can adjust the panniers fore/aft, and the way the load on top would not be restricted. Also, it has the top bed narrower than most, and the panniers sit "angled inwards" which should improve bike handling with heavy panniers.
Thanks again for all the feedback.