Reviews of this product?

[bwdz]

Those and other cheap Chinese made shocks are barely adequate for your minivan and have no business on a sports car. If you ever have a chance to look at the cheap tubing and pogo stick valving you will know why they have such a high failure rate. I put the Stagg on the back of an e36 once and they lasted only a few months and had terrible rebound (basically one stiff bounce with wheel hop that the car barely had with the aged stock units the Staggs replaced)

[bwdz]

Neal, to answer your questions: coilovers are struts and shocks in one unit where the coil spring is over the strut, they have adjustable threaded collars to move the spring to adjust the height of the car to your preferred setting. Springs are just springs, they go on your struts that you already have and lowering springs have a shorter installed height and often a higher rate of compression. The inside of a shock or strut is gas charged or oil, there is a piston inside a tube and valves that control how fast and smooth the piston can move up and down the tube absorbing the bumps in the road and making sure your wheel doesn't jump and lose contact with the road. Go to the website howitworks and look up how shocks work for an excellent graphic describing this process.
The price difference in struts stems from quality of materials to make the tubes and pistons and the complexity and sophistication of the valves inside to get the best rate of rebound and movement to soak up the bumps. Not always but the more you pay the more sophisticated they are and cheapies are made from cheap steel tubing instead of aluminum with just one simple gas valve inside just like they were back in the 60s when cars rode like crap.