Good to see home grown products but I'm not convinced.
If they were just progressive springs then that'd be fine (if they less than $90).
But 2 progressive springs at a cost which is nearly the same as 4 progressive springs,
lowering the rear by 20mm but not the front which will cause front end lift at high speed,
reduces steering effort by doing nothing to the steering end of the car!
Like I say, not convinced. When you get over about 15mph you don't need to give any extra effort to steer and at low speed, lowering the back of the car won't affect the steering weight.
They will improve cornering due to the lower stance and the progressive nature of the springs and that in turn will reduce the rocking in stop and go traffic (what we call "the dentist chair" effect) but they won't improve this any more than a set of 4 balanced progressive springs.