I bought this kit, thanks for trying it out Ares
. I installed the front as well. One thing I noticed in your picture, is the springs you installed on the back, are for the front. There is no way the wider coils that come in this kit, could fit under the top plate of the front suspension. With that being said, I'm going to need to order some rubber coil sleeves to put on the rear, as the factory bushings don't fit the wider springs. It's fine right now, but over time would probably cause squeaking. When I put on the just the rear, I drove briefly to turn my car around in my driveway, and the car felt odd being soft up front and firm in the back. With the whole set firm, the car rides wonderfully. You mentioned it still felt uneasy on the highway, replace the front and it will be more stable.
I second what Ares says, this is how the car should have come. To anyone who lives in an area with bad roads and or speed bumps (forgot the user's name on here, but had mentioned he had to drive REAL slow not to scrape) should definitely get these springs.
I have the stock ES wheels / tires, without any sway bar. This is my only suspension upgrade and the difference is huge. Body roll is reduced greatly, still there just not nearly as bad. I think the reason being the stiffer coils can recover from the rolling quicker, plus it doesn't roll as hard.
This has to be THE best bang for your buck upgrade I've ever done to a car. Just $45.
Be warned tho, if you're worried about your car not looking "cool" this does lift your car up. I don't have any before pictures to compare. I personally am function over form.