Hi,
This is an area that MS really need to im[prove on.
Even their official site listing the part doesn't state 'Active'
There are a few explanations below. Basically I gather that the signal is not converted to HDMI in the device (dock or Surface) but in the cable. Apple devices do the conversion in the device, not the cable.
That said, if you just need one monitor output, I've had little trouble. Unless outputting to a 75 and 86" interactive panel in which case sometimes Active is needed and sometimes passive.
In two years using this product I've not see a standard setup that works in all situations.
What is the difference between a passive and active DisplayPort converter? (startech.com)