Let me enlighten on something. Lowering springs are really no differant than sleeve type coilovers. The only differance is "coilovers" come with a height adjustable sleeve. BOTh come with springs, and in the case of Dropzone, probably the same spring for both, unless they offer a sport and race spring for the lowering ones. So saying coilovers make a differance, that's really not true, it's actually no different than a lowering spring, you can just adjust the height of the ride and usually the preload of the spring when the height is adjusted.
Did you install these on stock struts? If so I guarantee you that by this time next year if not much sooner, your opinion on them will change for the worse unless you upgrade the shocks as well. I don't know a single person EVER that didn't have a complaint once their coilovers/springs blew out their stock shocks. Plain and simple, they can't handle the increased performance of the lowering springs.