Hello,
The benefit of a single head 4K adapter is to run a 4K monitor or television. Because of falling price, their are increasingly popular.
The alternative is to use
two standard USB->DP adapters as the monitor you have is Full HD and therefore doesn't require a 4K adapter.
Alternatively, any of
these dual head docking stations using DisplayLink technology will be able to drive two of these monitors. Same number of cables, just connected to the box. The View Sonic VG 2439m has DisplayPort, HDMI and DVI inputs so even docking stations not being dual DP can be used.
MST has no impact on being able to do extended desktop or not.
I don't know what model of dock you have. We don't design or manufacture any end product, therefore contacting the manufacturer for confirmation would be better, but if I have the details I can look for you too.
Kind regards,
Alban