I work with someone who does great QA work. They know how to rip something apart, they understand the user's non-technical perspective and approach, and they understand what edge cases to look out and they have the actual equipment to test on different physical devices (and so on).

Most importantly, they have the diligence and patience to methodically test subtly different cases, which I frankly don't have.

On the question of whether QA slows things down, I have to ask: slows down what? Slows down releasing something broken? Why is that something to optimize for? We should always be asking how long it takes to release the right thing (indeed I'm most productive when I can close a ticket after concluding nothing is needed).