I'm behind the the *potential* Swift Springs kit which started as a result of there not being able to buy purpose-built springs for the Insight to improve its handling which I recently did on my Honda Fit and was very impressed. At first I contacted Ground Control but never heard back and also wasn't interested in lowering my Insight much so their offering was less attractive than the more simple springs-only kit that I talked to Swift about.
Since then, and with the help of others like Blue Civic Hybrid on this board, I've seen the value of the Ground Control setup since it offers the ability to swap between various standardized spring offerings AND you can tune the ride height, corner weight, etc. The Ground Control kit also has the advantage that Ground Control themselves are developing the kit. In the Swift case, I approached them about building a kit and they said they would as long as I can find 10 people to join me. We're close to getting the 10 people needed but I think a lot of us on that list would jump ship to the Ground Control kit if offered. Another advantage of the Ground Control kit is that you can get whatever springs you want (either when you order, I think, or afterward if your needs change) rather than having to go for the one-size-fits-all setup that the Swift kit would be. For those who want to add extra batteries or carry extra weight, that's a cool plus.
My understanding of the Ground Control kit is that it includes 4 springs made by Eibach w/slightly stiffer than stock rates and 4 adjustable spring perches that allow you to adjust the height of each corner of the car. It does not include shocks/struts. I'm working on a shock/strut solution (still just in the idea/research phase, nothing built yet) that ought to work with either kit or the stock springs.
