Ive had them on 2 of my cars and i have to say i was very impressed by them especially on my 200sx.
The earthing kit doesnt really do much but the stabilizer is good.
Basically the way its works i its stores pwoer in the box.
When you release the throttle and plant it again sometimes it takes a while to respond because you get a voltage drop and the stabilizer elimiinates it.
It made a really big difference on my 200sx and gave me 3 bhp on my previous civic
obviously theres a lot better stuff out there but i wouldnt say they were a complete waste of time