Hello,
As an UML tools user I have been using some of them very often. There is one thing that I have missed in all of them. The idea is what follows:
In the bar where you can find the compositions, association, ... and these kind of conectors, I have always needed a field in which you can choose both cardinalities of the following conections. I know you can do it manually doubleclicking on the connections but if you are going to have a lot of connections with the same cardinality, it can be annoying. Using what I say just help you to do it faster. You select the cardinality and you can start connecting things with the this default cardinality. Of course you can have a checkbox or something to desactivate it if someone does not want it.
Please if you read it comment about what is your opinion. I think is something that would make a difference with other UML tools.
Best regards,
Víctor.