Are these the ones you're using Phaedrus? [url=https://www.quickcandles.com/ProductDetails.asp?ProductCode=PM_1508_12]

How are they in terms of spilling and smashing? I like the idea of an 8 hour candle in my kits, and it looks like a good size, but I'm hesistant about the potential mess if things go wrong.

Those are the ones. Well, the container is plastic so of course it could be smashed. But they're small and cylindrical so they're pretty sturdy. Each one is capped with a very tight fitting "nipple" that's very tight. I've never seen a capped one leak in 20+ years, although it's not impossible. If you recap between burns you should be good. I keep the caps from dead ones just to have extras.

They easily burn 8, maybe more. And you can pull the wick up a bit to get a stronger flame at the expense of burn time.

You could use a vacuum sealer to seal these into individual bags to minimize the risk of a spill. If you do I'd use a low vacuum setting, basically just sealing more than evac'ing all the air.

In an emergency situation an 8 hour fire source can light a stubborn fire, and of course you can pour out the fuel if you need it.

So far I've never found the flawless, foolproof tool that was perfect for every situation. I consider this another tool in the toolbox, but one that I've used for decades and come to trust- under the right conditions.

BTW, one big advantage of these vs wax candles is that you can put them out and when you relight them the pick up right where they left off. With tealights you're often/usually better off burning them all in one shot. Very often the wick shifts and when you relight them the second burn is very poor. The paraffin ones are like having a flame with switch like a flashlight.