I have one of those blue Pivot voltage stabilizers and the grounding kit.
The grounding kit I believe helped with normalized electrical feed when the car's just idling in traffic. Without them my wipers were real slow while idling in traffic and sped up only when the engine sped up. With the grounding kit the wipers operated normally whether at idle or at speed.
You're right about the voltage stabilizer as probably being snake oil. Can't tell the difference with it online or offline.
I can understand grounding kits with modern or even semi-modern (pre-OBD-II engine management) making a difference, especially on older cars with dirty, corroding grounds. Not that I can explain it in any intelligible manner... I've been meaning to redo a lot of grounds in my engine bay just because they are all really skanky.