BMW electric water pumps are a lot more reliable than the mechanically driven models in the other 6 cylinders that last around 60K before you better replace it.
The electric pump is perfect for the application given higher volume when warm or hot and lower volume when cold or cooler out.
As is true with anything else in life BMW didn't build the pump, they out sourced it.
Also if you drive an E93 like I do the water pump isn't your biggest concern, the HPFP is.
$400 for the pump every 100K miles? OK well it isn't a cheap car and BMW as well as every German car I ever owned require maintenance.
I will step up to that and just enjoy the ride.
I know that I have been running Evan plus waterless coolant in my M3 for the last 3 years and in my diesel truck unpressurized for the last 7 years and have suffered zero issues regarding water pumps...