I did a write-up on this product in the beginning of this month - can run quagga routers in the UML image of your choice - wrote / ran a 12 router lab that ran on a p4 with 512MB / RAM. (http://www.vlcg.net/content/cloonix-clownix-rocks)
If this product was used - you would only be able to functionally test the protocols in a particular topology - wouldn't be cisco, and it wouldn't be the same as production (different protocols, different topologies).
I discovered this trying to figure out a way to run quagga in a gns3-like setup. GNS3 is great for testing a specific cisco thing that you need to learn about - but it didn't do well for me beyond 3 routers - (too much hand-holding getting the environment tweaked).
My ultimate vision for quagga would be to run it on the hypervisor and let it scale (in numbers of routing instances) wrt to the number of hypervisors - it's a pipe dream for now, but I think that routing that can scale with hypervisors is going to be a big challenge for cisco (esp if they try to do it in silicon) -