I used to sell loads of Gaz coilover kits, quality is 'ok' on the badic kits, better than the usual ebay, Jom, raceland, Gmax 'insert ebay brand name here' type tat. Did have an issue with seal failure many years ago but I am sure they have solved that now.
The high end kits are very nice, But for the cash I feel there are better options.