After research i came to the conclusion to buy an 5400. My HP 8570p notebook supports displayport 1.2, thus it should work. (http://h20628.www2.hp.com/km-ext/kmcsdirect/emr_na-c03565466-1.pdf).
After connecting the MST, i connect one display using DVI and one display using a displayport to VGA adapter (active conversion). What happened was that only one monitor showed up in Windows and the other monitor became a mirror of this monitor.
I’m guessing the problem could be active converters to VGA, on the other hand: might my laptop be not sufficient? It has an intel HD4000 display chipset. Nowhere is it absolutely clear if this chipset supports multi-lane displayport. Looking at the intel documentation (https://software.intel.com/en-us/articles/quick-reference-guide-to-intel-processor-graphics) it appears at most 3 monitors are supported on the HD4000. Yet the limit seems to be two.
1: does my laptop support the MST5400 at all?
2: are active converters to VGA not supported? (does the MST know this at all)
3: do i need active converters to VGA, or are there passive ones where the MST converts the signal?
4: did i forget to install certain drivers, control panels or other stuff?