I don't know about Sportline..but the Tien springs (the SS series) rides very well and gives your a car a very aggressive look. I live in Milwaukee (which are the second worst streets in USA next to Detroit in my opinion) and besides some craters my car rides over bumps and holes very smoothly. I've rode in my other cars with just springs and let me tell you my Tien/Focus combo is the best I've rode in yet. The car turns great and handles very well. The stock struts and shocks also ride well with the springs but if you do hit a large bump or crater it does have a spring affect on the car (but that's what you'd expect with all cars with just lowering springs).
If you're wondering about the drop, it was about 1 1/2 drop. So it wasn't too big, which is good if you don't want to scrap the bottom of your car or door panels.