Besides the AW IMR, there are very few nipple top batteries coming out anymore. One isn't "more" safe than the other to my knowledge. In fact, I had a meltdown once BECAUSE of the a flat top battery. I have a prototype Caravela Latina drip tank that had a small screw that fastened the hybrid base to the tank and was not recessed. It hangs down a little inside the tube. When I put a flat top battery in the 'Vela, the wide flat top contacted both the center pin, and that screw, which was ground. That tube started getting hot lickety split and I was able to dump the batt before runaway. Just melted a little of the wrapper but I picked it up with an oven mitt and threw it outside. Stayed hot for quite awhile but never vented.
In a hybrid cap, all it takes is for the center pin to push above the outside thread, and boom. 510 drip atty's have the center post only press fit into delrin. It is quite easy to screw them down hard enough to push that pin up beyond the base. Bashiks Prometey and some other models have a center pin that is just friction fit. The idea was to make it adjustable. You can pull it out with a pin to make it longer, but by the exact same logic, screwing it down directly onto a battery can push it up flush with the base. Boom.
I had another bat that didn't have any wrapper curled around the bottom. The whole bottom was bare. Some mech mods back in the day didn't have an insulator on the bottom button. Screwed on the bottom, and instant short. Again, got it out in time and tossed it out with the oven mitt.
ESTABLISHED builders have come a long way to foresee and prevent these kinda things, but my point is even if you know what you are doing, there is the potential for things to go wrong. NEW builders are coming out with new devices every day, and may or may not know what they're doing.
The biggest danger I see on the market right now is TC devices. No, they are safe in themselves, but these ultra low Ni200 and Titanium builds that they require to work are a disaster waiting to happen. Say I have 2 kayfuns, and I build one for TC at .15 ohms. I have another with Kanthal laying around. I pick up the wrong one, the .15 ohm, and screw it onto an 18350 mech mod with a fresh battery. When I hit that button, it's 118 watts and 28 amps surging through that batt. I don't think there is an 18350 battery on the market that can handle that. And some guys build down below 0.1 for TC.
As an avid motorcyclist, you keep prepared by reminding yourself.. It's not if, it's when.