Hi.
Personally I would use proper lowed spring kit, there work properly as they should because they've been designed to. And safer to.
The clamps are a cheap way of doing it, but I wouldn't recommend it. And I'm sure others would say the same.
Oh.... And if you were to have an accident, and it was found that the spring clamps were to blame because it made the car behave in way it was designed to, not only would your insurance company have an instant excuse for not paying you a penny out in comp, if the police were involved, they could procecute you for having a vehicle not in a safe condition.
Not saying it will happen, and hope it doesn't, most sevear case I know, but a really good reason for not going the clamp route would be if you value your life, and your friends / family, I'd go the proper spring kit route.
If you look on other threads, there is other advice about lowering, and it appears that down 35mm less on standard shocks okay, any further and good idea to get matching shocks to. May as well if your changing the springs at the same time ?!.
But as always, ...... the choice is yours chap.
Drive safe
