100% this. I've used AWS emulation layers for local-first development going on the better part of a decade. I cannot stress how much time it saves me from pushing code that would have failed in staging. When the cost of deployment pipelines via cloudformation is so high, it's a no brainer.

DIY mocks alone can get you somewhat there, but that relies on the developer having intimate knowledge of the aws sdk under test and it's very easy to mock the inputs and outputs wrong. I'd rather defer that to an emulation layer that does that mimicry better than my guess and check with 30m between attempts when my cloudformation deployments ultimately fail...