The classical spacers are replaced with a “magnetic” spacer, which is the reason that the wheels shine. (These special spacers are included).
(Ofcourse you still need bearings, like all the other wheels.)
It is quite normal that some LEDs are shining less after some time (because normally LEDs are used on an office table and not on a wheel for jumping and sliding).
Grip of the wheels: you will be amazed.
Speed: the additional resistance is quite low when you are riding at normal speed.