Are you asking about licensing? As far as that goes, Three20 is licensed under the Apache license.
Apache license: http://www.apache.org/licenses/LICENSE-2.0
Three20 license: https://github.com/facebook/three20/blob/master/LICENSE
Or are you more interested in whether bugs get fixed timely, community support, etc? If so, I've generally found it to be pretty well-supported, although the documentation isn't great. Installing it/the size of the dependency used to be an issue, but this has been addressed by breaking the libraries up into chunks and also scripting adding Three20 as a depdendency. The code is certainly solid as is evidenced by the fact that Facebook's iOS app is written on top of it.
Hope that helps