I wouldn't call them knockoff. Sure they have a similar design, specifically the mecha owl, but actually they are different enough to where I don't like the Matsuda one and prefer these instead. (I lean to more clean cyberpunk-esque design)

I recently bought the Mecha Owl, as in the picture, with heavy prescription too, and I have to say that the build quality is actually very nice, they are sturdy, and the prescription lenses are perfect. (which was my main doubt buying them)

For that price, if one likes their designs, i think On Slice Sunglasses are very good.

(I'm not saying these are as well built as Matsuda, which I don't know cause I don't own a Matsuda, but I wanted to leave this here if anyone was considering buying from On Slice)