I recently bought the Touratech X Low Seat. I had a standard 2014 GS seat. I took a 12" ruler and with the bike in the center stand, ruler at the lowest point, measured from the ruler to the footpeg bracket (in my case 20").
Then I measured the Touratech X Low Seat using the same method. It was 19".
So the X Low Seat brings you 1" closer to the ground. Another factor to consider is seat width. The Touratech seat is narrower so you get better "reach" to the ground.
The seat is hard (not a concern for me) and you do feel like you are sitting "on the frame rails", again not a problem for me. I find that I can now flatfoot one foot comfortably almost anywhere. Both feet down I'm on the balls of my feet and still quite comfortable, before it was tippy toes.
Overall good choice for me. YMMV