Ive brought JOM from ebay £180 free P+P, had them for over a year now, not one problem.
Remember once fitted you have to give it time to settle in, you cant drive over speed bumps like before, you have to go much slower and depending on how low your car is you may have to go over speed bumps on one side of your car not through the middle as youll probably hit something underneath.
Some companies also provide 1yr warrenty, coilovers feel alot harder then springs but once settled in the ride wont feel as harsh.
Some people go for out and out low, bad thing about doing that is you have to be careful of every bump in the road and weight eg more passengers most likely your wheels will be rubbing against the arch, other people just make sure theres a tiny gap between arch and tyre not noticeable, with this you dont need to worry about weight and you can drive fast knowing that nothing will brake, stiil have to be careful of the bumps.
More often its just luck when purchasing suspension parts, so long as its fitted correctly and you drive sensibly they should last a while, also after fitting its best to get tracking done a little while after.
Good luck