I'd stay away from Brooks leather saddles on a Stromer. The ST1 already has a very steep seat tube angle and I had to get another seatpost with a lot more setback plus run my saddle as far back as possible in order to get my position dialed in. Brooks tends to run with the saddle rail range more aft than most other saddles, including Stromer's stock saddle. As a result, you may not be able to get a leather Brooks pushed back far enough to get the right fit. The C Series works fine though. I ran a C17s on mine and it worked fine. The saddle does have a hammock effect and adds to comfort a bit.
Tai