Whats the idea behind twisted keys? seems like a strange idea to have hex keys that are pre-damaged...lol
I dunno what the physics are, but those are so damn cool-looking I just might have to get a set.
Maybe the idea is that they expand slightly when you really crank on them? Dunno.
And yeah, ball ends aren't as strong as a straight end. Seems completely obvious there's a tradeoff there.
Sometimes a ball end is the only way to reach something, but usually you crack it loose with the straight end and then run it out with the ball.
The Wiha and Bondhus ball ends with the fastener holders are an incredible time and frustration saver, but again, it's fairly obvious there's a tradeoff in strength. They have a specific purpose of making disassembly and assembly easier, but they're very obviously not meant for final torquing or cracking loose stuck fasteners.
Those stubby keys are quite nice too -- I've had to make my own more than once.
And yes, if you deal with socket head fasteners much, you will need a variety of hex key tools. It's like any other type of fastener; the correct answer to "which tool" is "ALL OF THEM!"