When increasing power you put more strain on other parts of the car which also need to be upgraded, when guys talk about breaking drive shafts 9/10 they mean the knuckle (join) breaks up. Inside there knuckle you have this tripod looking thing with bearings and it's normally the bearings that go. I think it's very unlikely to actually snap a shaft.
This just doesn't apply to increased power, it's also the intended use, if you track or drag race your car you may also break a rear axle.
These are aftermarket shafts which should handle just about as much power you can throw at them.
This kit does no include the tiny intermediate shaft, it is not as common to break one of them.
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Next upgrade would be the gearbox itself, it is rumored that the 5 speed is stronger than the 6 speed because they have thicker gears but they still have their limitations. This is a very pricey upgrade though. I doubt i will replace the box, i will most likely upgrade the gears with an aftermarket solution and get them Cryo treated which is a process that involves freezing components to -200c.