Ride quality is similar to stock (comfort mode). Sport mode it stiffens up a decent amount. There a more noticeable difference between the modes now. Hope this helps :)
When my sensor got disconnected, my car was stuck in "sport mode" all the time. So it was relatively stiff for daily driving...
I had the HKS set installed this past weekend and I'm surprised you can't tell any difference stock vs post-install. To me, the car feels significantly stiffer and I can feel the bumps etc. Not in a horrible way, as the car feels more responsive, but it defintitely wasn't as cushy as comfort...