Peugeot 207 - Sport Helesion Spring

Friends A friend who wants to buy a sports helicopter bow for 207. I know the eibach brand with high quality but there is a Performance brand spring like 550TL , they looked 250TL , they are all written in `` special alloy steel '' metal, so it is the same in raw materials ... so what is the reason for the price difference between them? If it is 50-100TL, there is no problem, but when there is a 2-fold price difference, people are wondering.

the difference comes out

1 life (you can use it for a long time without losing its feature according to the product quality)
2 hardness (depending on the model, the hardness changes, some feel comfortable in kw, some are softness in other brands, in other words)
In 3 eibaches, the top of the hose was inserted, which softens hitting in hard pits.