Mixing various contact enhancer?? Craig/Walker/VDH

There are quite a few contact enhancers available from different companies. eg: VDH, Craig, Walker, Xtreme Quick Silver.

If I have applied on product already and like to try the product from another comapny, do I need to clean off the contact surface first by some special chemical???

Or a combination of different product will yeild better or negative effect? I guess you can never clean the stuff out that is left inside an AC outlet, so they are mixed at that contact point anyway, right?

Thanks for your input.