Not really. Even something as small as maximizing your tor browser window can indicate to whoever's watching that you're one of N people using that same screen resolution.
And sure, N is pretty big for popular websites. But the less popular the site, the less it holds up.
Tor is about the most effective thing we have, but I'm not sure "really effective" is fair. It gets the job done sometimes, but it also leaves a lot to be desired.
Still, I'm grateful Tor exists.