And why does the 1050 FME have such a wide variance in the idle speed - surely that's not good if you don't employ some form of speed control ?

The way I read that is that you can set the speed anywhere between 10,000 & 29.000 but that would be a no load speed ie at idle. soon as you put some load on the spindle it will slow, the amount it will slow will depend on the load & as there is no speed control the drop is not compensated for.