Im using the exact same Decklink Mini Monitor 4K and Flanders too, and its fairly reliable in AE and Premiere, the 4K model is much better than the older Mini Monitor that i experienced some trouble with.
I would say that for simple output only its not worth to invest in the more hardcore decklinks anymore, i had a 4K extreme that i 99% of the time just used as an output card and went the 4K Mini Monitor model and havn't noticed any worse performance than before.
Unfortunately with the way Adobe has implemented the Mercury Transmit in AE and Premiere its far from as nice and smooth to work with as in Resolve. Adobe tries to switch resolution all the time so expect a lot of loss of SDI signal with the Flanders when you open anything not within spec to the decklink or the Flanders monitor.
In Resolve you set a fixed output res+framerate and everything will be scaled to this, resulting in a much much smoother experience.
btw... there is a bug in either the current AE or the latest BM drivers, that will loose the output signal after some minutes working in a comp, then you need to force an update by switching to another comp with a supported res and back again, then the Transmit output updates.
all in all, a semi nice experience, but 100% nessesary for all work i do.
Robert