Brass checks are great when there is light to see the brass.
To assure a round has loaded, you touch the top round in your mag and determine if it is sitting to the left, or right, then you load up, eject mag, feel for the round and if it is still on the same side, you don't have a round chambered.
This is what our former DEVGRU, current-Federal agency trainer drills into us when we reload and we do it always with our eyes closed, which trains you to use the same physical motions always to reload, regardless of being able to watch/see while loading.
FWIW.