Not only is it scientific, not only is it science, it is the scientific method. Or rather, Marxism (dialectical materialism) as a philosophy contains the scientific method - as a justified part of a whole philosophy, rather than a free-floating 'neat idea' as it is for capitalist scientists.

To a dialectical materialist, the only way to understand the world, i.e. develop a theory about it, is through practice in the world. Practice and theory form an inseparable dialectical union. Make a theory, test it in practice, revise the theory, revise the tests, iterate again and again until you can fully describe the phenomenon you're studying.

Marx and Engels expressed this as part of the philosophy of dialectical materialism, an advancement beyond Hegel's dialectical idealism, and then used these methods to study economic relations and the society that results from them. But dialectical materialism goes beyond the theories of political economy that Marx developed using it, even if the search for answers about political economy was what caused Marx to develop it in the first place.

If this formula (theorize, test, theorize) seems completely obvious as the only way to generate knowledge about the world, it's only because most competing philosophies of knowledge have fallen by the wayside. But even so, this is not actually the dominant understanding in the world today, because all bourgeoise science eventually has to blind itself to reality, smudge its own results and ignore the real explanations of phenomena in order to justify its own existence. And even when scientists do manage to follow this method, either through principle or in a field that capitalist ideology doesn't need to corrupt, an understanding of dialectics gives it a much deeper and richer meaning.

Only under dialectical materialism, the proper philosophy of the working class, is true science even possible. And the results speak for themselves, because an advantage in creating true knowledge about the world gives an advantage in controlling the phenomena of the world, so throughout history, socialist nations have made strides in scientific progress, matched by strides in industial progress, far in advance of what the capitalists can achieve.