Ranked in these QuestionsQuestion Ranking
Con Overly verbose
The one item everyone who likes Quick promotes is how it describes your tests. But in actual fact it's a false pro. Firstly it takes several nested levels of blocks to do it. That's more boiler plate that's not needed. Secondly, Quick uses those descriptions to create dynamic test methods with huge method names which are a waste of time. No-one reads the method names in the test reports and they're too wide to display in the test navigator to be of any use.
Finally, the descriptions are only as good as the developer writing them. Having these long descriptions of a test doesn't automagically make the test any better or the author a better developer.
Con Encourages bad programming practices
Because Quick only has one method, all of the tests are written in this one method. Problems that stem from that include huge amounts of code in the one method (there've been over 2,000 lines in some), very deep nesting of blocks within blocks, tests that depend on other tests, and all sorts of other problems including things like hours trying to resolve merge issues because a bracket was removed from a block inside seven other blocks in a thousand line method.
Con Breaks Xcode's unit test support
This is applicable to any test framework that builds tests dynamically. Basically run again, test filtering, and most of Xcode's test support doesn't work. Plus Quick forcibly takes over the test meaning that you cannot run it along side XC tests either.