You do not need 2 pumps... 2 pumps will give you some peace of mind that if one pump fails the other will be running BUT... you can just buy a PWM version of the pump instead of the Vario version and if the pump fails the computer will alarm. Also you said that noise was of the upmost importance too you... I would highly recommend you buy the PWM version of that pump instead of the Vario.
Also if you must run 2 pumps http://martinsliquidlab.org/
showed that having different pumps was actually better than having 2 identical pumps (noise wise) and that having 2 different pumps did not at all hinder performance of either of the pumps. So essentially you can run a smaller cheaper pump as a secondary pump if you are that worried and don't want to spend a bunch of money. Personally I think it complicates the build and increases the price when those pumps are fairly reliable.
I don't know of a reason why you wouldn't be able to use the mayhems aurora... did you see something that worried you?
Cost was a concern... I personally don't see Mayhems as anything but a cosmetic item. I don't see how it could perform better than distilled water with something like swiftech hydrx added to it.
Especially since you may end up taking the loop apart and having to flush it early on. Also to my knowledge the non-conductive claim is just because they are using distilled water and it does not stay non conductive as it picks up ions and impurities while in your loop. I have spilled fresh distilled water on electrical devices with no issue and I have seen phones completely submerged in it. It is no special trick that the fluid has to be able to do that.
If it makes you feel better then get it... but seriously there are tons of tests that point to you basically paying for expensive colored water that makes you feel better... Also expensive fluid causes some people to not want to flush the system as often which is not a good idea.Edited by givmedew - 7/2/13 at 2:35pm