If they add some sort of sand box, or HIPS, and get there detection rate up it might be usable. Signature based detection just does not cut it anymore.
They are saying they are offering Sandbox in free - maybe it's not implemented yet? HIPS is available in Pro (play with the app - I found it).
Tried to go to MDL and hit the URLs - it blocked every single one of them for me (toolbar screen with Security Warning). I tested all of the freshest ones - it's working for me. The bad thing though is that it lets you continue to the site if you want to! It should prevent users and not give them the option.
Wasn't brave enough to attempt to run malware on there nor did I have the time (setting up VMs).