Just a little question I have. What are the benefits of having the shields on the bearing? Will it make the bearing last longer, reduce the chances of something getting on the bearing, or what? And is it bad to not have the shields on the bearing? Thanks! 
Benefits of having the shields off: Easier to do maintenance because you don’t have to take them off and put them back on.
OK, sure, maybe it’s easier for something to get into the bearing, but stuff really has to get all the way down into that yoyo to get near the bearing. It’s slim but probably and CAN happen. If it does, clean out the bearing. Oh, wait, that’s not a big deal, you already have the shields out!!
Having the shields on or off won’t affect bearing life. Many people choose to not re-shield their bearings. I like my bearings shielded whenever possible, it’s just my choice.
My son’s Protostar, SHIELDED bearing, still got clogged with bits of hair from playing in a barber college.
Do which-ever makes you feel best. It’s all your choice and no worries either way.
I think it just reduces the chances of getting dirt or debris ending up inside the bearing.