I've had a couple of Astras (a SxS double shotgun and a "Constable" DA .32 auto) and am always impressed by their innovations on other peoples' original designs--the Spanish have always done this. I think it has something to do with European patent laws--their patents expire in ten years, and Spanish gunmakers have almost always come out with their "take" on other designers' guns shortly after that period is up.
Sometimes they are actually improvements. I like the design of the Constable better than the Walther PP that it is clearly related to, and the Browning Hi-Power takedown system that Star added to the original Browning 1911 design in their "Super" series of full-sized SA autos. 1911 ergonomics with an easy takedown.
Is your A90 related to a SIG design? Please let us know how it performs if you decide to shoot it, and THANKS for posting!