Well, I would advice you have a play about with meteor and make the judgement yourself. It really depends on what you wish to develop
Certain constraints I have found are
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Meteor comes bundled with only mongodb. Other database support are planned for later releases
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No model/object form binding (in road map)
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Package system is not npm (although Meteor is built on node) and is closed to community. All meteor packages are developed by meteor themselves
Regarding performance, I found this article helpful
Here is another link to meteors roadmap
From my experience, I would say the advantages I have found outweigh any disadvantages at the moment