Popular because of their durabillity and their good price. Zealous bearings are greased and they can handle water pretty well. perfect for training! You don't have to wash them as then the grease would go away then. Just skate them through all the shit and make sure to spin them every now and then. They might get a little louder after some skating, but they will continue to roll.
 
Good for all the budget skaters out there!