The Bont 688 mini bearing has an exceptionally fine polished bearing track surface and incredibly precise balls. The lightweight plastic cages allow for lower rolling resistance. The extremely strong steel helps the skate bearing keep its shape when under load.
Note: that this is a 688 mini bearing, which fits an 8mm axle and a wheel with a 688 mini hub like the Bont FX1. To use these bearings with a normal 608 hub you'll need a bearing adapter as well.