Negative throttle values?

I' ve seen and used negative throttle values in configs allthough I allways feared negative rotor spin.
What' s the hidden logic of negative throttle values?

Not exactly sure of your question. Is it that Deviation uses 0 as the mid-channel value, with -100 as the minimum and +100 as the maximum? Never used Spektrum but from what I've read they use 0 as minimum, 50 as mid-stick, and 100 as maximum. And stock Devo firmware does too (?).

Exactly. It' s not a technical but a semantic issue. I know 'full throttle' (100%) and 'half throttle' (50%); never heard of 'negative throttle' (-100%).
But I am not a native speaker.

I think it's more that the sticks operate on a -100 to +100 range, and that should be standard across the sticks; why make "throttle" operate on a different scale than the others, when each stick is really independant of the end result? On a 1-to-1, no scaling, straight-out-to-the-channel setting you will get exactly the same servo pulse of 1ms minimum to 2ms maximum regardless of whether it says -100 to +100 or 0 to +100. You usually need to calibrate ESC's to your output range anyway, so it doesn't usually matter a damn what the value is saying on screen.

Though most vehicles here use only "positive" throttle, plently of other vehicles would use negative, eg. cars, and even some "3d" quadcopters.

If the representation bothers you, you could just make a virtual channel that takes the inputs and converts them to a 0-100 range, and have that display in a box somewhere. You an even output that new value range to the channel and recalibrate your ESC. Thought; do you now only have 100 steps of throttle rather than 200? Or is it actually spitting out 1024 or 2048 values? I dunno.

Some Tx's do everything 0-100, which makes a throttle of 0 mean no power, which makes sense. But then "neutral" on the rudder, elevator an ailerons is 50, which doesn't make sense. Some do everything -100-100, so that neutral on the rudder, elevator and ailerons is 0, which makes sense. But then - as you observed - to get no power to the engine, you need the throttle at -100. A few apparently do both, labelling the throttle as 0-100 and the other controls as -100-100, which makes each make sense individually, but can be confusing when you have mixes.

Since deviation doesn't really know which output is the throttle - as it varies depending on the protocol, and even that isn't reliable for these RTF craft! - it really can't do the last one. With the power of the mixer in deviation, having values go from -100 to 100 makes a lot of things easier to do, though I don't know if that's why that option was taken.