Telelogic Tau modeller

I'm interested in experiences with the Telelogic Tau modeller.

My team are currently starting elaboration on a medium sized project.
Our current tool is Rational Rose, but not all of the team are
trained.

We have been offered Tau but I'm worried how long it will take to
become productive on this new tool.

I'd also be interested in hearing about the advantages of Tau over
Rational Rose Modeller.

Thanks

Tim

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