Not to say these might also not be duds. I've purchase and returned 3 different 4K monitors (UP2414Q, U28D590D, LG 31MU97) so far, each had either a compatibility issue or a display quality issue. Dell has an extended holiday return policy that makes it less risky, but if you're in doubt, wait till the first batch of these end up in people hands in a week or two and there should be a bunch of comments, positive or negative on the forums.
My expectation is we see similar quality to the other 4K IPS Dell monitors without the issues
from their first generation MST design.
One word of caution - if you're someone who frequently switches between boot drives by holding down the option key - 4K SST monitors currently interfere with this because they don't light up until the login screen. If you can't live with losing this feature, don't buy any 4K SST monitor until this is fixed.