The spring rates for the Evo 8 can actually be found in the application chart. They are given as 4.4 kg/mm front and 5.7 kg/mm rear. That's roughly 25% harder than stock. Probably not too bad, as the hydraulics setting in the dampers tend to be hard and the springs soft (you know, when you drive over a speed bump it's hard, but when you enter a corner fast the car rolls a lot).
The part that makes me unsure is the "down rate". Appearently given in inches, this seems to be the drop in ride height after fitting these springs. As you can see, the front is lowered by 1.5 inches and the rear by one inch. This alters the car's weight distribution and necessarily increases the stress on the front struts.
From a handling point of view, this altered weight distribution combined with the much harder rear springs will give the car more oversteer under WOT
That's not a newbie setup, but can be more fun for the enthusiast for 300 bucks.
You should be aware that the stock struts are a simple dual tube construction made out of low spec material, that the oil quantity in them isnt huge and that they may start to leak after hard use, especially if you autocross. If you just drive to work, you should be fine. Although 1.5 inches is a significant reduction in damper travel... your decision!