Quite disappointing. Dock for SP3 was also very fiddly. Some miniDP-to-DVI adapters that would work directly on SP3 miniDP port just didn't work on dock, and in the most spectacular way - SP3 would freeze during the boot process every now and then. But at least Apple's miniDP-to-DVI did work well - kind of ironic, isn't it? Anyway... with SP3 dock, we figured out dual screen with any two DVI monitors with little help of EVGA DisplayPort hub, and reasonably straight cabling including generic miniDP-DP cable (between dock and hub) and 2x DP-DVI cables between hub and monitors. SP3 screen could be used as 3rd screen, so there was extra benefit. Hub also had 3rd DP output, but we never tried 3 desktop screens. Should work, though - maybe at expense of SP3's native screen.
Now with SP4 dock... we were hoping that MS will improve on multi-screen support, but alas. We have tried all sort of minDP-DVI adapters, no success. With Apple's adapter, we could get one screen work and clone or extend with default SP4 screen; but adding 2nd desktop screen would actually dissable the one that work and SP4 would see only one screen - its own.
Dock for SP4 costs NZ$260 and is, at this stage, nothing but $260 brick. Beside that, MS choice of ports is annoying. Situation is likely better in US, but some other parts of the world, NZ included - it is hard to find miniDP-DVI cables, as well as reasonably priced monitors with DP... so we have to use additional adapters that add to price and complexity. MS would really do us all a favor if they made brick a bit bigger and put two full size DP ports. MiniDP has place on Surface itself, where real estate is limited... but dock, not at all. Every other dock I have seen recently - HP, Acer, Lenovo - have standard VGA, DVI, full size DP... even HDMI on some of them.