This is the ceramic-bearing version of Wheels Manufacturing’s external bearing bottom bracket. It's suitable for use with all Shimano and Race Face cranks and some, though not all, FSA cranks (those with a tapered axle will not work). It comes with spacers so it can be used on 68 or 73mm BB shells.
Ceramic ball bearings are harder than steel ones (roughly double on the Vickers hardness rating). They also generally have a smoother surface ﬁnish and up to 40 percent lighter weight than comparable steel balls.
The harder nature of the ceramic bearings means they’re less likely to deform under load and thus will retain their roundness – with the rule of thumb being ‘the rounder the better’ for any ball bearing.
A smoother surface means less power-robbing friction, and lighter weight means less force is required to make the bearing move and also less energy to propel the unit forwards.
What you feel is a temporary sense of the cranks spinning more freely – that is, until you become desensitised to the feeling. After that, riding is the same hard work it always was.
The reality is that it’s taking you a fraction less energy to spin the cranks just once, and those fractions soon add up, though it must be said the effect works as much on your state of mind – knowing everything is as smooth running as it can be – as it does on extending your actual physical ability.