It doesn't work for everyone, but it does help some people. Frankly, it can depend on the quality of the SLP. It can also depend on the individual being treated. Stuttering is complex; what works for one person does not work for everyone. The same goes for DAF and masking, it can help, but it doesn't help everyone. For some it's perfect. For some it moderately reduces stuttering over the long term. For others it has very little effect. Do what works best for you, but it's absurd to say that all SLPs are useless because you had a bad experience. The same goes for basically any other treatment. None of them work for everyone. That's why talk of a cure is crowned upon.