There are no progressive springs on the market. Rockjock, savvy, Currie, Rancho... doesn't matter they are all going to follow physics the same. Companies can vary spring rate by changing the pitch, or the distance between the coils. And while it's true for every pitch change, there is a spring rate change, when the spring is compressed they all average out to a single linear rate. Research dual and triple spring coil-overs if you want to understand more. Doesn't matter if there are two, three, or four pitch changes. The only time a spring can actually change rates is when one coil collapses onto another coil, then both of the touching coils are removed from consideration. Then, and only then, the remaining coils determine the overall spring rate.
As for the MC spring, it would have been more accurate and say "linear spring with a build-in tender coil".
The only thing dumb about the MC spring is that in the rear it limits up travel more than necessary. If your shock is going to limit up travel before the spring, then it doesn't matter. It's just another bent steel rod, just like the rest.