I’m a big fan of Sigma lenses - I’ve owned and used lots professionally, but this is one that won’t get beyond testing.
Maybe I was unlucky, and just got a bad one, but results from this Sigma 18-35 were very poor. Full aperture tests were very, very soft - especially at the wide end. Stopped well down performance was just about OK, but not nearly as good as most Sigmas I’ve owned. Build quality is fairly lightweight, lots of plastic, but perfectly useable. Sigma make lots of excellent lenses, but it appears this just isn’t one of them.
In short I’d say the Sigma 18-35mm f3.5-4.5 is best avoided. As a cheap wide option the Tokina 19-35 is much better.