Spacer lifts are not recommended in these. You are better going to a decent spring and strut combination like old man emu make. These kits are matched to spring and dampers and the ride quality actually improves in my opinion.
While you can use a strut spacer in the front, what are you planning on using in the rear? You can fit a spring spacer but will need longer shock absorbers.as the existing will be running in a position that doesn't leave much extension available.
Remember any lift may need camber bolts and lower control arm bushes and CV joints will wear excessively once you get over 40 mm lift
Expect to replace lower control arms within 12 months of doing a lift if they are original as the bushes will fail.
The folks in at this place make what is equal to a 54mm life. I assume it is just springs and in no way different than what anyone else offers.
I personally run a 30mm and I had the same issues 2013GV talked about. Replaced the lower control arm, bushings, driver CV shaft and tie rods due to them already being worn in at the stock ride hight.
My 30mm lift is a spacer lift and I cannot say that my ride has had any negative effects. In the long run I will likely experience spring sag and the springs will ether compress or my ride will suffer. No telling how long it will take for me to see the negative effects but it has been over a year now with no negative results under normal driving conditions.
Under extreme driving conditions you will do damage to the spacers. I have pushed the suspension to its limits by jumping the vehicle into the air. The rear spacer did loose it's shape and required me to remove it and repair the spacer. If you can find aluminum spacers it would be better.