The gap at the slide to barrel allows you to visually confirm if it's loaded. You can see part of the rim of the case. Don't worry about a "blow out" as the rim and just above the rim on the case is solid and the part of the case that isn't solid is still supported by the walls of the chamber.
My P09 had the glow in the dark sights, not real tritium night sights. Hit them with a bright flashlight before stepping outside in the dark and they'll still glow for hours. On the other hand, if you figure you won't have warning/time to light them up between needing them and using them you might want to put real tritium night sights in it like I did on my P07.