Eibach is fantastic almost no difference over bumpy roads and car just feels more planted.
I got the 30mm kit not the 40mm front and 30mm back.
As long as you also dont go to 18" wheels LOL that makes you feel it abit.
They cant void warranty for springs as you can buy them from directly from opel Germany, so i wouldn't be to concerned about that and as far as rims go the adam comes with 18" and its the same suspension. So if they do complain i will fight them on that fact. It has also been in to dealer for a diff problem and they didn't complain about it. If you google eibach you can get the local dealer in JHB where the kit comes from anyway.