The TW Flo colors we get are concentrated. They aren't really meant to be printed straight. They do settle to the bottom as stated and need to be mixed regularly to keep them alive (if not you'll need a drill+paint mixer+water). The powders you get from a place like nazdar are actually better. The powders do not grey other colors as much if you are mixing them into other things. Therefore they look cleaner. But the powders do not go as far, price-wise, as the concentrates. If it's just flor-ink vs flor powder heads on, you cannot really tell the difference.
As far as drying in, there really isn't much difference either. You should always prewet your screen regardless of what WB color you are printing. We don't use retarder very often because we print fast and don't want to wait any longer than we have to for ink to dry. If you are a slow printer that doesn't have to worry about when you are printing the next color then retarding the ink will be helpful