I know both the "Berekuil" as well as the "cycle roundabout" as they are both down here in Eindhoven.
The Berekuil is nice, but very confusing as to what direction to go as you no longer can see the roads once you are down in there.
The floating cycle roundabout OTOH is fantastic as you keep having a great overview. It really is a marvel of engineering.
The slope is not a problem on either of them for the average bicyclist in the Netherlands.
edit: Just noticed that the referenced Berekuil above is another one in Utrecht. I meant this one [1]
[1] https://en.wikipedia.org/wiki/Berenkuil,_Eindhoven